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 bad 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.