warped transmission pan????

[Tom 260E]

I took my 1989 260e to a MB independent shop here in Scottsdale, AZ to address a transmission fluid leak. This same shop had rebuilt the trans 16 months earlier and it has operated great with exception of the recent leak. I thought it was the pan gasket so I serviced transmission myself with new filter, pan gasket, etc. the trans continued to leak so I brought it to the shop as mentioned above. My wife picked up the car (mistake!) after they said it was done. I talked with them over the phone and they told me the pan was warped and that it is not uncommon for them to do this after remove/install several times. I brought the car home and it still leaked. I checked it out and narrowed it down to the dipstick fill tube. I took it back in and they replaced the $.85 o-ring and told me "no charge". I was hot and told him I thought the warped pan diagnosis was wrong and I was out the cost of the pan. He stood behind his mechanic and said the pan was contributing to the problem. Anybody else have problems getting the pan to seal after trans has been serviced more than a couple times? please tell me what you think. Tom