1991 350SDL approx. 240k

Since I have owned the car (last 50k) there was a few seconds delay from selecting reverse gear to engaging reverse gear. In the last few weeks the time was noticeably longer. Yesterday it would not engage reverse at idle no matter how long I waited, even with a warm car. I have found that it will engage if I raise the rpm's above 2000, (and then it chirps the tires).

The fluid is up to the full mark on the dip stick when warm.

I have an extra transmission sitting around, but if there is any easier fix...

Thanks,
Greg

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO