Hello! I have had my 1983 300D for 2 years now, but I've had a worsening transmission issue since my first drives in the wintertime. My issue first started in December of 2021, when it got to about 35F as a low in the mornings. Shifted fine from 1-2 and 2-3 but 3-4 would have a consistent slip/grab feeling until I let off the throttle, and then it fixed itself for the day. This happened without worsening until it got warmer in the spring, and it didn't happen again until November of 2022. The problem began to get significantly worse as the winter has progressed, and for the first 15-20 minutes of driving after the engine is cold, my 3-4 shift has a strange slipping pattern that gets worse with throttle, and 2-3 also acts up early in the first drive when cold.

I feel like this isn't the traditional "slipping" that is described in auto transmissions, especially since it goes away until the engine goes cold again after I have driven for a bit

See attached video of the tachometer readings while this slipping happens

https://youtu.be/FmoJdG2BEOw

Any advice would be appreciated. Thanks!