Much of game RSD is based on the viability of the original design (or redesign in term of electronics of MMr or AFMr).
SMD for boards can be a reliable alternative, if augmented with through hole components in critical sections that require specific redundancy. Those PCBs that do not have it, are considered completely disposable in the industry today, as the time spent by technicians today for repair often does not offset pure replacement costs, if the technicians even have the skills to do the work.
No owner should be believe that a game will not have problems, as this is pinball, and the number one rule often broken.
Pinball as a whole has more potential for issues than many other types of amusements or vending, with the exception of some pieces of redemption equipment. Don't place your faith in a corner and cross fingers.
Being that I work on both the MM, MMr, AFM, AFMr, and still own an original MM since 2004 (when I finally decided to justify the purchase, and kept the game running ever since), I lean towards the WMS game for many reasons which I presented in the past, outside of the current potential near term problems on the WPC95 A/V Board.
People should consider how many original MMs come up for sale now. Playfields and parts can be replaced, if needed. Collectors already knew and brokers are now hard pressed to acquire them since the end of the reimport era in 2005. But, why does an potential owner really want the game, and how much are they willing to pay to get the example they want? I cannot answer these two questions.