So, typical of 1983 models, my mechanic replaced the entire engine wire harness. Only now the engine temperature gauge doesn't work. We argued about causation: it worked before he redid the wiring; he thinks that something else caused it. Film at 11. The previous owners didn't know what a flame trap or oil trap were. Both were impacted with dried oil. It took 3 hours of soaking in carburetor cleaner and a screwdriver to open up a hole in the sludge in the oil trap. Volvo was nice enough to sell me a new one, in the meanwhile for $30 (damn piece of plastic!). Now the car idles like a kitten and drives much smoother. I'm hoping that the valve cover gasket oil leak and rear main oil seal leaks will resolve now that the cause of the back-pressured/increased pressure has been resolved. I'll keep a close eye on both and keep you updated.