Something else to look at, pull the valve cover, take a look for any sludge buildup. This will happen when the previous owner(s) didn't do their required maintenance, and/or used shitty oil.
Start using Mobil1 Extended Life High Mileage or Pennzoil Ultra Platinum along with Mazda LF05-14-302B filters. If you do have sludge, do frequent changes, those oils are so good, it'll clean right up.
I had bought a well used 168k mile 2000 Honda CR-V, and doing that same thing, had terrific results. I had to drop the oil pan at 200k because of a stripped drain plug, ana I swear, it was so clean inside, you could have eaten off of the engine.
Same thing happened with my 2004 MZ3: pulled the valve cover at 200k, and it was like brand spanking new. Just absolutely clean.
One last thing: the MZ5's like yours are known to have oil coolers that will leak oil. Pull the bottom engine cover off and inspect it. It lives directly on top of the oil filter housing. That very well could be the cause of your smells.
At the time of the last compression pressure test a week ago, there still was positive pressure in the crankcase trying to lift up the oil fill cap.
After another week, and the oil smell does not seem to be coming back. Additionally, unscrewing the oil cap and trying to pull it out while the engine is idling shows that there is now a vacuum in the crankcase too, which indicates that the blowby issue has disappeared! The compression pressure seems to be about the same, roughly 155 psi when warm, so I don't know if that's going to improve, but the crankcase vacuum is still very encouraging. No leaks observed near the oil filter or any other engine gasket. I haven't pulled the valve cover, but it looks pretty clean through the oil fill cap hole with a flashlight.
Additionally, the "new" used Mazda 6 wheels now have tires and are installed (although Discount Tire really screwed up the fresh paint on them - they handled the painted winter wheels for two other cars fine, but these got really beat up), the brake system is flushed, and I went through the various plastic panels and heat shields to add foam and other sound-deadening material. At this point, Kaylee is feeling like a new car!
I may go down that route at some point too - in this case I was looking for panels that would make noise if I shook or hit them, and applied foam weather-stripping or felt-tape to the back to deaden the vibrations. The main culprits were the cowl panel around the wipers, the rear part of the front wheel wells, and the undertray, although a few of the heat shields were also loose or had torn away from their mounting bolts so some nice big fender washers and a bit of bending got them more firmly mounted too.
I had to repair the lock mechanism in one of the sliding doors right after we got our 12. There is ZERO sound deadening in those big doors! NONE. When I get those done, I think that's going to make a huge difference right there.