98 S70 Auto transmission not going into reverse

[billjohnson121]

If the PNP switch is bad, will it prevent the tranny from going into any other gear or just reverse? If it's the tranny that's going bad are there any other symptoms that will tell me it's the tranny and not the PNP switch? Going down the road, it shifts like a dream; there are no bad noises or clunks coming from it at all. Fluid is a little dark, but not bad. If it is the tranny, what is recommended to troubleshoot it? Not going into reverse is only intermittent. I talked the local shop and they said if I bring it in and it goes into reverse, there's nothing they can do because it's not broken then. If I do want to have someone open up the tranny and troubleshoot it, what is involved with that? Is there an oil pan that they can access the insides or does it get more involved than that just to diagnose it? 145,000 miles on the odometer.