i purchased a motor from a guy says it was rebuilt. how can i really tell. said there are about 5000 miles on the rebuild. this was a complete rebuild bore out .020, the nine yards. so today i pulled off the valve cover looks great very clean maybe a new rocker arm ass. but i am questioning bc the spark plugs had a bit of residue on them nothing real bad but were moist. said the motor really hasnt been driven on in 9 months this is an oily residue by the way. also i took a light and looked at the top of all the pistons through the plug holes everyone of them had moist oil on top of them starting from the #1 which was the dirtiest and #6 was the cleanest. i heard it run sounded fine. i checked all push rods rockers and nothin was loose. what do you think?