[mcf1000x2003]

I have 95 STS with magnaflow mufflers with camaro tips and I notice every couple of days my rear bumper starts turning black right above the left tip. The guy at the muffler shop said there may be something wrong with my motor or something cuz its never suppose to get black like that.Can anyone tell what i can do to stop this? The car is still running great but i get annoyed having a black spot that makes my diamond white paint look like crap.

 

[mcf1000x2003]

I bought the car with 102k and it has 107k on it now im not sure if it's ever been tuned but it still runs smooth and strong.I usually go to work with it which is a 10 minute drive exept on sundays when i drive around for 2 hours dropping off papers.

 

[mcf1000x2003]

No codes on the ECM exept everytime i cold start the car the it says check oil levels even tho my oil level is ok.Im getting pretty crappy gas mileage about 12-14 in the city and on a 200 mile trip i took a couple weeks ago (all highway) i only avg. 21 mpg