"the oil level as indicated on the dip stick fluctuates somewhat erratically. I have had the experience, more than once, of checking the oil and the reading indicating I am more than 1 quart low. Add a quart, and then check it again, and the oil level is over the full line"
Had some experience with this - it can mean that the engine has a lot of gunk in it (you had a second hand, not rebuilt!) so that the oil does not always flow back properly to the sump/oil pump - which may not help keep oil pressure up, and may lead to excessive wear and serious damage. The oil heats, and expands, as does the passages, so the oil flow can be slower than normal, when adding, or checking, but will usually flow down eventually.
When this symptom appears, I did an 'engine flush', which means you put a special detergent additive in for a short while before the oil change, helps 'flush out the gunk'.
I did run a car for ages with a minor oil leak, cause the clowns damaged the oil sump plug sealing washer... eventually insisted that it be replaced, and the leaks stopped...
This was with cars that were 'simple mechanical' - no 'car computer', so can't help with that side ... repairs there can be expensive and nasty ... it seems that older 'newer cars' are less tolerant of 'aging gracefully'.