I posted here a few months ago because the automatic transmission in my '87 w124 had stopped shifting up smoothly (especially at less than full throttle).
I took it to my mechanic last month and after checking the vacuum system they determined that the cause was a defective vacuum 'switch' in the transmission. It was replaced last week. They had to get an MB mechanic in after hours to get things working properly, but now everything runs smoothly again. The switch cost 75 EUR excl tax and the whole repair cost me 190 EUR.
Regards, Peter