Barry Weeks knows the answer,it's a design flaw of the oiling system.The old timers used to trash can the hydraulic lifters,put in a set of solids,the cam didn't seem to care,nothing wore out or was clackier that normal.
A 235 has several large oil drain holes in the rear main cap area between the rear bearing and seal so oil pressure can never get at the rear seal.
There is no after market high volume pump for 235's,you can use a 228-302 GMC oil pump to give more oil flow if needed.
