PLAN OF ATTACK
1) Yesterday I replaced all the fluid by dropping 3.5 litres then using Gibbons method to drain about another 6 litres while refilling at 2 litre increments. This took about 2 hours because it was often just a trickle and sometimes was not pumping at all
I was using clear hose to drain and I could see that the fluid was struggling to get up the hose and into my container marked at 2 litres. Fluid was filthy black at first.
2) PHASE ONE, ESTABLISHING THAT THERE IS A BLOCKAGE
Blew compressed air back through the cooler through the hose and managed to get normal pressures back to the drain hose. I had UNBLOCKED THE FILTER!! Temporarily unblocked I might add. FINALLY the turbine-like noise was gone and wheels were turning with force in both Drive and Reverse while up on stands. Left it up on stands with engine running for another 30 minutes. No strange whining noise present. Wheels were still turning with great strength against the brakes in Drive. Took it for a quick spin and was great. After a longer drive (2kms) the noise re-appeared and the car slowed to a crawl. The filter had blocked again

3) HOW DO I UNBLOCK A BLOCKED TRANSMISSION FILTER?
Nautic_01 gave me an idea when he showed photos of the rebuild on his own 2001 T5 auto last month (what a great write-up on MVS!)
The filter on these AW55-50/51SNs is a one-way design. It is simply an in and out design slung low in the lowest part of the transmission where heavy sediment from friction surfaces can settle without contacting the valve body. If fluid can't reach the outlet port of the filter, there is no flow of fluid through the valve body so nothing will work; no Drive or Reverse.
If somehow a solvent can be pumped through the transmission to clear the blockage in the filter perhaps the sediment can be removed?? However when the transmission is blocked nothing flows through; not even solvent. So do be able to start the process of a filter flush I must first unblock the filter with compressed air through a hose connected to the top cooling port on the radiator as I previously did above.
4) USING SOLVENTS THROUGH THE TRANSMISSION
THREE DIFFERENT PRODUCTS CONSIDERED:
1) Kerosine at Hardware Store
2) Parts cleaner at Auto Parts Store
3) Hydrocarbon based cleaners-Shellite or wax and dust removers
Kerosine is cheaper than all the above items however it leaves an oily residue. I don't want this residue on the friction surfaces as it may not interact well with the transmission fluid.
Parts Cleaner-the particular parts cleaner I look at smelled, felt and tasted like Kerosine (that's a joke of course). In fact the description was the same: petroleum distillate and was retailing at twice the cost of Kerosine at Auto stores. Sounds like a major rip-off.
Hydrocarbon based cleaner-this is basically the same stuff as fuel system cleaner. It does the job of cleaning sediment from my sump after an oil drain. Cost is high but worth it. A 4 litre container is around $30 at a hardware store over here. It shifts dirt and grease without leaving any residue at all. It won't melt plastics like turpentine and acetone can do. It's safe around all the plastic connectors in the valve body of course. I've been using it for years as a general de-greaser/cleaner for electronic clutches, nylon gear assemblies and cleaning of rubber components where a film such as paper dust or general grime has collected preventing the original frictional properties of the rubber.
5) FLASH POINT OF SOLVENT: WILL IT CAUSE A FIRE OR EXPLOSION WITHIN THE TRANSMISSION?
Yes the flash point of solvents is much lower than transmission fluid however it will be used at roughly a 50% mix with transmission fluid and pumped while the engine and transmission are very cold into a container on the ground. Once about 3-4 litres is pumped out it will be replaced with transmission fluid and then gradually diluted with another drain from the upper cooling port.
TOTAL PARTS LIST:
1) 4 LITRES (OR QUARTS) OF HYDROCARBON CLEANER
2) 12 LITRES (OR QUARTS) OF JWS3309 COMPLIANT FLUID. USE WHAT YOU LIKE HOWEVER SYNTHETIC FLUID FROM PENRITE AND NULON HAVE DONE WONDERS FOR ALL OF OUR TRANSMISSIONS. PENRITE AND NULON DON'T MARKET IN THE USA AS FAR AS I AM AWARE SO GO SHOPPING FOR SOMETHING BETTER. I'VE HEARD GOOD THINGS ABOUT VALVOLINE SYNTHETIC FLUID
3) 1.25 METRES OF 8MM INTERNAL DIAMETER PLASTIC HOSE FOR DRAINAGE
4) 600MM OF 8MM INTERNAL DIAMETER PLASTIC HOSE FOR FILLING
5) ELECTRICAL TAPE FOR INCREASING THE DIAMETER OF THE PLASTIC HOSE WHERE IT MEETS THE UPPER TRANSMISSION COOLER PORT TO PREVENT LEAKS
6) COMPRESSED AIR NOZZLE TO TEMPORARILY UNBLOCK FILTER. YOU CAN BUY COMPRESSED AIR IN A CAN IF ON A BUDGET
7) 24mm RING SPANNER FOR DRAIN PLUG

So I put 4 litres of solvent into the transmission after draining 3.5 litres from the drain plug. At first it seemed to come out quite dirty however on the first drain it went straight into a dark oil container. On the second drain I used my drain pan and I could see it was more or less clean. It really wasn't bring out as much sediment as I'd hoped.
The wheels still wouldn't turn in drive while up on stands. So I blew compressed air in to the radiator port through a hose and voila the wheels began to turn again. This time I managed to drive for about 2kms and luckily returned to our home when the pressure was beginning to falter.
Upon looking at the design and shape of the filter I can see why it's hard to push the sediment out because of the upward design of the upper outlet spout on the filter. Sediment can't travel against gravity unless it's caught in suspension with the fluid and this doesn't happen in practice.
So to all the gurus who understand chemistry far better than I ever will: What liquid will attract heavy metallic particles and carry it away in a suspended form?
Hopefully this will lead to the cure!!