I attached a page from the Owners Manual for a Chris Craft Commander;  the 10hp model.  They make mention of “grease” as opposed to “oil” but they make no additional recommendations.

I think you would be fine using something like Lubriplate 105 or John Deere Corn head grease.  I have had excellent results with either of those two in direct drive (non-shift) gearcases.  The Corn Head grease might be cheaper so I’d probably go with that.

It can be injected with a squeeze tube or a grease gun.  Pump it into the lower opening until it oozes out the top.  It might push some old grease out first.  That’s good.

PS:  Do you have spark?  I would check spark and compression.  A good way to evaluate the general health of a motor before spending a lot of money.

Hi Q,

These pages came from a search I did the other day;  looking for anything at all on the Chris Craft motors.  These were “Sample” pages from a website that was selling the “manual” for $35.00.  A PDF  for $35!  The sample pages were free…..but they are not of very good quality.  I attached a PDF for you.   Good luck with your Challenger.

Chuck