i only use my car in the fall and winter therefore my tires look brand new but are five years old,do i need to replace them? also i use my boyfriends car as my daily driver which is a 91 eclipse with a 2.0 automatic has 110,000 miles,i've been putting a quart of marvel mystery oil at every oil for over a year now,i noticed the engine not only feel better(feels looser)but top speed has gone up from 100mph to 110going uphill to 117mph on a flat road.i want to try it in my t2 mainly for the rubber seals and carbon build-up and acid formation,what do you think?

 

Not sure about the tire question, but as far as the marvel mystery oil, I use it in my 88GXL and don't see any negative side affects. My car pulls strong and revs very freely.