That said, I still don't understand your post. The best I can figure out is that after 1000 miles, your car doesn't run well because it's dirty? I don't really understand

What Thinfourth is saying is that he can't bear to see his new pride and joy dirty so he has to clean it, and every time he sees his new pride and joy clean he feels the urge to drive it, thus making it dirty again. This is a problem because his insurance policy is only valid for 5000 miles per year(*), and at the current mileage rate is going to be invalid in about 32 days time leaving him with a car that he cannot drive for another 325 days.

(*) This is a popular option for sporty/expensive 2nd cars, where the annual premium would otherwise be extortionate.