722.3 losing third gear & won't engage
 

Hello enthusiasts I recently put a 1987 300E back on the road and have been driving it to work daily. When I get on the highway and drive early in the morning when the engine/transmission is cold it shifts fine from Second to Third and will pull without issues. After driving 20 minutes or so the transmission will slip third gear and rev free until it goes back to second gear. I almost moneyshifted the car today when going 100km/h after I let go of the throttle and the engine rev to about 70rpm had to drive 70km/h at 4k rpm for another 10 minutes in second gear! The fluid level is good and was changed last year at jiffy lube from previous owner should I start there or is this sign that my trans is out? I never had trans issues on my 190E 2.3 and its over 250,000km. So far I have adjusted the bowden cable and ordered a new Modulator but I doubt this will fix this issue. Does this mean rebuild time? Here is a video