The Mark 5 is a wonderful motor, and a real performer for it’s 5 hp. class, but this is the largest and most common issue with them! The gear cases are very prone to water intrusion, and this is what happens. I have seen a ton of these with this problem, and I have a case that I have welded up now. I am still working on getting the threads repaired after the welding, as you need penetration to get a good weld, and this usually damages the threads. This is a left hand thread housing, and they are hard to come by. As you still have the broken off part, take it to a sheet metal shop that does aluminum work and see if someone will weld it for you, but be wary of the risk to the threads. If you can find another housing, that is the best option, but it is not always something you can find, as like I said, the Mark 5 and Mark 6 use the same basic housing and they are all prone to this damage.
Steve
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