I just bought a 91 K75 with only 15K miles. I'm very pleased but it does hesitate a bit and is smoking some. A couple buddies of mine say it probably has a old seal that's going or gone and the fuel injectors are gummed up. They suggest some injector cleaner and to take to a shop for some maintenance. I would like to know if those are good suggestions and going forward should I use dino oil or synthetic?