Within a second or two the engine is idling about 1100rpm. If I put the trans in R or D the transmission doesn't engage. After about 5 or 6 seconds you can feel the trans engage and everything is fine. If I leave the trans in Park for 5 to 6 seconds and then put the trans in D or R it will engage in about 1 sec which is normal for this trans and a lot of others I have driven.
If everything is working as it should, the torque converter will not drain back. There are check valves in the valve body and front pump to prevent this from happening. It can also be caused by bad seals. The check valve in the transmission cooler line will help if one of the other check valves is leaking. It is worth a try because the next thing is to remove and repair/rebuild the unit. The man recommending this has been a transmission specialist for 30+ years. He has worked on a lot of these transmissions. He recommends doing the check valve first, then go to plan B if it doesn't help. Sounds like a good plan to me. I'll let you know if it works or not.

Paul

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84 500 SEL (307,xxx miles)