Looking to get a 88' M5 our same model 535is what are the differences between the two besides the motor? Also what is the going price these days for a runof the mill 88' M5? I can pick up the 535is for $2500. Also are there mods worth doing to the 535is? If I were to get it? and How hard is it to find an 88' M5 with the black interior instead of the tan?