if you're filling in key marks, just sand it down to the metal. everything should be OK.

As far as scratch removal priming, you need a self etching primer to make a good bond to the metal and a filler primer to add layers to be sanded off.

But yeah, like Hyper25 said, you don't need bondo for a key mark.



There's alot of different techniques to painting. They can all be used with or without each other.

 

Sounds like you dont have much of a problem so you really wont need any bondo, but you might want to get somethin more light weight and easier to sand for anything else you might come across in you journey, i would recomened putty coat sands easy too...Dont get glazing putty it might bleed through...Also when you are doing the key holes dont take it down to bare metal if it isnt that bad sand with 220 and use a high build primer...sand prime sand prime ect.....Thats if it isnt bad....