Cobra Outdrive Lockring issue?

[robcurtiss]

I recently purchased a 1989 boat with a 3.0L and Cobra outdrive. The previous owner revealed to me that in the past year, bearings in the outdrive were replaced. He then showed me the Clymer repair manual, where it shows disassembling the upper gear housing. He commented that he did not recall removing, nor installing, the 'lockring' that is shown in figure 14 (page 403). He has run the boat since without issue. I have not gotten the boat into the water yet, but it runs fine and I have minimally engaged the propeller.

Should I be worried about this? The guy was very honest with the boat and I trust him as much as I could a guy I'm buying a used anything from.