E400 trans. delay of 6 to 8 sec in rev.

Bought my 93 E400 used and had everything including trans serviced - just because. Trans seemed ok. After about 15,000 miles a delay developed when shifting into reverse. Now it takes about 6 to 8 seconds and one has to be carefull so as not to be too hasty because it slams in hard.
I have researched the site and did see an old posting about a modification that might help.
Any new information?
150,000 on the car.