I had a 40 year old car that was rarely serviced but ran like a champ. I moved across country and the new mechanic told me I should use some cleansing agent to de-gunk all of the various hoses/manifolds/whatever in the engine. It seemed expensive so I went for to a second mechanic and mentioned it, and he was adamant that I not do it, and that all that gunk was what was sealing the hoses and letting the car operate.

I took his advice and drove the car for another 10 years before donating it.

Maybe something similar happened there? Maybe he had scabs that we're ugly but protective - they got scrubbed off, and then his body had to deal with a whole new wave of pathogens.