1992 Toyota Camry Problems, problems!

I purchased my car from my sister who had purchased it from the original owner a few years back. It Had been in a left front collision and was repaired but since we've had it, the transmission is slow. The car runs good, but before takeoff and gear is on drive, the takeoff is slow, no power to move faster. I would usually put it on low gear (L)for it to takeoff and shift to second (S) to feel the gears shifting and from there I can put it on drive (D) and for as long as i'm on the go without stopping the car is okay. What would be causing this problem? Would I need to change to a new transmission which would be very costly. Another "new" problem its having is oil gets into the spark plugs causing the car to jerk and die out. What would be causing this problem and how do I handle this? Am I having some sort of oil leak somewhere? Please help for I am in a bind and in need of transportation.