Re: rebuild instructions for pre-alpha hydraulic trim pump
After hitting a sand bar (depth finder malfunctioning, bow queen wasn't watching

) the second time I ever drove my new old boat (my first boat ever) on vacation several things happened...leaking trim cylinder first, couldn't patch it or afford replacement, so a "boat mechanic" in Ocean City said to just use brake line plugs at the dist. block on transom to eliminate that cylinder...boat will trim fine with one cylinder...this worked for 30 seconds on trailer. After running up and down twice things working so far but third time going up "blam" ! loud pop and fluid spraying violently by trim pump...I think I just blew the line...last day of vaca so I leave it be and spend time with family.
Once I get it home I order hoses and 2 trim cylinders on ebay (originals were old and corroded) guy said he has pump also for $75...that it will probably go soon also. I figured for $300 replace the whole system for insurance. After installing everything, now no leak but trouble going up.
I read, read and read some more (thanks Don for the manual) I discover the majic o-rings. Soooo just to be curious I replace the o-ring in my old pump, reinstall old pump (they sell kits on mercstuff.com $15 or so for all gaskets/ o-rings) put the drive in forward (not running) to make the reverse lock position change on shift plate and presto everything works great! Now I have 2 complete pumps.
Here's the short answer...I believe you can get an o-ring (if yours is indeed blown) either from mercstuff OR maybe from a local hardware store (take yours to match) and your back in business after 5 minutes it takes to remove dog bone and replace o-ring and the .50 cost for the o-rings. It may not hurt to take reservoir off and clean out and there's a screen under the metal cylinder that could use cleaning, also not hard to do.
From what I've read and seen here I DO NOT recommend rebuilding...lots of small PITA parts to lose or reinstall incorrectly, not worth $75 for the trouble.
Wish I knew all this a year ago but welcome to boating! Thanks to all who've helped me here, I'm quickly understanding the workings of my new hobby.