In my experience the shift shaft seal (O-ring) is often the first to go and even though it is only an O-ring….the gearcase has to be split to replace it.
I usually do that after I get the engine up and running; no point to invest in a bunch of seals if the motor has some other “fatal flaw”
Member Ben Breitner has done a great series on servicing OMC engines; here is one of his series on gearcase R&R:
https://youtu.be/BRgcg4haPuo?si=K4xsTiOEzKRtAXyV
There is a simple tool made to remove the shift shaft seal bushing. A MUST HAVE.
0304514 Shift Rod Bushing Service / Removal Tool
