Is my local cadillac dealer inflating issues with my 03 DTS?

[Walachka]

Last week I went to car dealer to attempt to get an inspection but my service engine light was on, they made me pay $50 to see what issue was and the service guy claimed it was my torque converter on my tranny and that it was slipping very badly and soon wouldn't pull, price $2-$3,000. I said no, I also remember a while back a different service guy told me it could only be minor and that it may not be getting enough pressure and only $300 anyways when I was on highway yesterday i noticed my service engine light was no longer on and hasn't returned yet... This makes me think it's a bad sensor not my tranny becuz my car has 117k miles and rides extremely smooth, I'm starting to question my local dealer, especially when this certain service guy approaches me the bill is always some outrageous repair in the thousands, the last time I went they claimed my car was leaking oil from like 20 places and said I needed a $2,000 engine reseal, yet I only put a quart of oil in my car a month.. but do you all think they r pulling my leg and that I should begin to avoid this dealer? Car has been far from neglected I've followed all service dates in manual spent over $2000 with this dealer within 2 years