I have a 1955 Evinrude that I am trying to restore that slips out of forward when running. It does not have this problem in reverse. When you put pressure on the shift lever in forward it does not slip out. The gears do not seem to be grinding. Are there any adjustments for the shift link or the shift lever to solve this problem or do I need to tear down the lower unit to see if the gears are damaged. Any help trouble shooting this would be greatly appreciated.