I have a 2000 Jetta GL 2.0 w/automatic transmission. This was my wife's car, she was the first owner, and it's been mine now since she got a minivan for the kids. It now has 90K miles on it and shifting has always felt good, never noticed anything wrong or off with the transmission. Recently, trans fluid started dripping. I took it to mechanic and they replaced oil cooler O-rings. The mech said he had to put in some new trans fluid since it had leaked a bit. Said he used Pentosin-1. After this repair, I have noticed it's beginning to slip from 2nd to 3rd and 3rd to 4th. It doesn't do it all the time, very infrequently but noticeable when it does. My mechanic says this is probably because of the new oil he put in and recommended another mechanic to check the transmission since he doesn't do that work. He said I should nurse it while driving, which I am doing, but that I should fix it soon since it can get worse and more expensive to repair later. I've always had cars with manual transmissions so I'm pretty worried. Does anyone have an idea how much this repair might cost? Also, the car has 100K miles engine and powertrain warranty with VW but since I've never taken it to the dealer for maintenance I'm worried they might tell me I had to replace the O-rings with them and that I've voided the warranty. Any thoughts on this would be appreciated.

 

Before anything, get your transmission fluid changed. After that, put a bottle of Lucas Oil anti-slip fluid in it. I think because your o-rings were leaking it's probably got some clogged lines.