Still Running Hot

My son and dad picked Kim up last Friday and took her home... she had to get back to work. I've stayed with the boat and my new friend Greg the mechanic, we've spent a lot of time together the last few days.
When we pulled in here last Thursday Greg and the marina owner, Chris, were quick to help. First thing we discovered was the fact there was very little coolant left in the heat-exchanger, the reason was due to a blown gasket where the heat-exchanger end cap attaches to the heat-exchanger housing. Greg tried making repairs but eventually had to pull the heat-exchanger and take it to the shop... it was very difficult to work on it in the small engine compartment while standing on his head.
The heat-exchanger housing, where it mates to the end cap, was dented and fouled from some previous (can't really say mechanic so I'll use the word dumb-ass) dumb-asses work. After damaging the housing dumb-ass had trouble getting a good seal so he used a lot of silicone (a paste that dries to a rubbery consistency) to get a tight fit. This worked until I reached Columbus Marina where it sprang a small leak when running hot. For some reason it never ran hot again until we reached Bay Springs at the top of our last lock, Whitten.
Chris came up with a very good resolution to the problem, he crafted a small aluminum spacer and obtained a slightly thicker O'ring, When mating the end cap back to the housing he installed the O'ring then the spacer then the end cap then a little silicone, the spacer applied enough pressure to the O'ring to make a good strong seal. When we performed a sea trial it held however the engine still ran hot.
So far we have inspected the through-hull, the strainer, the impeller and the oil-cooler. Everything looked good until the oil-cooler, it has kidney-stones. Well, they are some kind of calcium type chunks and there's a lot of them. Greg also fished out a two inch long strip of something that looks like duct tape, although it's not duct tape... just looks similiar. With everything cleaned out Greg replaced the plug and we did another sea-trial, looked real good initially but then started running hot again. We came back and Greg found quite a few more stones in the oil-cooler.
Tomorrow morning (10/8) he's going to pull the oil-cooler and take it to the shop where it will be flushed with some type of solvent. This is the only way I can have confidence that it's clean. This little problem is getting to be very expensive but the good news is that my old job has requested I return on 10/27 as a contractor to assist with a software upgrade. Worst case senario is that I leave the boat here for a few months, possibly all winter.