Lionel Legacy CP GP30 engine 6-28557 from 2007 catalog
Problem is both motor mount screws are stripped in the front engine. The holes in the die cast frame are probably also stripped. Rear engine screws are holding OK but screws are damaged and should probably be replaced also. Lionel does not offer replacement screws for this engine and earlier ones. I have determined that the screws are round head M3 x 6mm long. Lionel changed motor mounts and went to M3 x 8 mm long screws after this. I would be better off with 8mm long screws since the 6 mm ones don't go all the way through the frame and there is room if they protrude the extra 2mm.
I plan to get some m3 and m3.5 screws in 8 mm lengths. If the holes are stripped it is not feasible to try ideal solutions like inserts or any kind of rethreading and drilling. I would likely damage something else in the engine. I hope to try the larger 3.5 screw if this is the case. Maybe some Loctite or some other adhesive? Concern is that the motor mount gets quite a bit of force when the trucks are locked in.
