Even a good running 4100 will never be reliable (they can go down hill very quickly, because one problem can cascade into multiple), and the time and effort into repairing them usually doesn't pay off like it would other engines (because you can never fix anything back to 100%, and again, one small problem can break everything). But that doesn't mean you or anyone else should just replace it; it means that the 4100 should not be trusted, and it should be expected to break at any given moment.
So when getting a 4100, you should have contingencies lined up; you should have good roadside assistance, a second and more reliable car, and know a garage that can do engine rebuilds or replacements. If your 4100 dies, you can swap it with an Oldsmobile 307 or a Chevrolet 305, without having to change anything else in the car, so it may be a good idea to have an extra engine (or know where you can get one).
When I got my 4100, I got everything in line, except the second engine, because I didn't expect it to take a shit after 200 miles, but now I know better
Just keep in mind that depend on climate and the amount of driving the car sees it can still have dampness on the oil filler cap just from normal condensation in the engine. Ive seen several cars over the years and even had a few of my own that would constantly have a build up in there even with nothing wrong. Then driving habits change or the car passes to a different owner who uses it differently and it clears up completely.On my first 4100 I monitored the coolant leak possibility by checking the oil filler cap every week. If not leaking, the underside of the cap should be dark brown or black and dry. If leaking, it will be light brown and damp. If found damp, you must STOP driving the car and at a minimum replace the intake gaskets ASAP!
To be honest, the engine was pretty much dead when I got it, but things got so much worse so quickly. The only mistake I made was trying to drive it after finding out there was no compression on the #8 cylinder, and that didn't really contribute it completely breaking down like it did (maybe it was a variable). What really started it, was a blown radiator, which caused the thermostat housing to fail (even though I had a radiator shop replace everything), and then right after that, the fuel system crapped out.Did you drive it pedal to the metal all of the time? Any motor can take a dump if you abuse them.