W210 E300 Transmission S mode Problem

[kinghais]

My E300 shifts hard when it's in S mode, specially from 1st to 2nd. sometimes when I'm slowing down it shifts really bad from 2nd to 1st (when first time this happened i thought got hit from the back!) like horse kick.
I'm not sure if it has anything to do with oil service. I wasnt able to check the oil cause it has no dip stick.
when I switch it to W mode it shifts fine like No signs of shifting hard at all.
I searched about it but i couldn't find anything. I'm having this problem since last year. help me out guys I don't wanna visit Stealer.