940 Transmission Issue

[pizzaparty1]

I have a 1995 Volvo 940 Wagom with about 202,000 and the transmission was making a high pitched whining noise and slips and I decided to change. I have just changed the transmission with a used tranny that I bought from a junkyard. We completed the work it ran great and then after sitting in the driveway for a half hour or so it was slipping and seemed to be pretty much dead. One very relable mechanic mentioned to me that it could very likely be a bit of antifreeze that was still present in the system either in the line or the torque converter. I just think its to much of a coincidence that the second transmission is doing the same thing. I really dont remember if we used the "new" torque converter from the junkyard or the older one that was giving us the original problem. I have had several opinions and of course its really time consuming to drop the transmission and start again. I have seen many responses for and against flushing the auto transmissions on the 940 but would someone be so kind as to comment that is a reliable resource on this topic. I would love to flush and change screen etc and be good to go but Im not sure the best way to flush the system. Most Volvo mechanics that you talk to say that this tranny is bulletproof and rarely go..... Thanks for your help!!