How did you get on with fixing the 30A electronize speed controller? From what you said it sounds like a relay problem to me and so replacement of one or both of the relays should fix it. You used to be able to get an external relay version of that controller which had the relays removed from the board and the relay coil wires brought out. You provided external relays [12 v coil] and wired the relays across the output to form an H bridge. This was much better than the internal relays because:
1. You could provide heavier external relays which were less likely to fail.
2. When they did fail you could easily test them, find the defective one, dump it and plug in a new one.