First, I do not take in new customers often, as I am generally booked six months ahead. I am a new member and I was prompted to join this forum after a bad experience I had with a well known shop. So since I joined I might as well make some contributions.
I worked at the Mooney factory and know these birds pretty well. What I see a lot of when a new customer brings a Mooney into my shop is that:
1. The landing gear pucks are often the originals from the factory.. I have seen pucks with dates from 1963 to 1967 many times.
2. The hydraulic hose for the flaps is also very often the original hose.
3. Brake Rotors
We all know that Mooney's can be prone to leaks and there is only two ways to fix them. 1. Have the tanks re-sealed or 2. Install bladders. Leaking cannot really be prevented... they will leak at some point in time, but replacing those pucks before they loose their resiliency will prolong those leaks. Mooney recommends replacing those pucks every five years, but you can probably safely go seven years, depending on the climate your aircraft is in. So if you own or are thinking about buying a Mooney, check the date stamp on those pucks.
The hydraulic hose is another one that seems to never get replaced. After a while those hoses become brittle and start to deteriorate, sending little peices of rubber through the flap system.. that's not good. You can change that hose out with a teflon hose. The cost is not too much greater than replacing it with the same Strat-o-flex or Aeroquip hose. The best part is that every five years for about $40 you can send that hose in to be inspected and re-certified for another five years. The same goes with the engine hoses.
I see a lot of brake rotors that for some reason most shops seem to miss that they are below thickness tolerances. It takes a long time for a brake rotor on an aircraft to wear down to that point, but I see it a lot.