I just picked up a Sea Raider - I also noticed that the Control Motor often runs a little bit too long (which doesn't allow the credit button to start the game).
I believe the issue is related to the 0-degree Position Switch B (which is a make/break switch). My guess at this point is that it's out of adjustment. I've attached the relevant part of the schematic (the full soft-copy can be found at https://drive.google.com/open?id=1aGdTbRsqx-Z1Njrq80G4zTIbvPPe2AD9). I'll post again once I figure it out for sure.
Sea Raider Control Motor (resized).jpg