I did my own solid state conversion using the original can and an NTE 1953 regulator chip (about $5 at the local electronics house). Still working fine after 5 years or so. (I have an early TR4 temp gauge in my TR3.)
However, what I discovered is that the chip needs a capacitor on the input, which many conversion instructions do not mention. Without the cap, it was oscillating, which caused the chip to appear to be bad. In one case it overheated and shut down during testing on the bench, the second attempt with another chip seemed to work fine until I got it in the car but then appeared to only be putting out 8 volts. The NTE datasheet doesn't really mention the requirement for the cap, but two caps (one on input, one on output) are specified in the "electrical characteristics" section of the datasheet.
https://www.nteinc.com/specs/1900to1999/pdf/nte1953.pdf
I don't know which chip the Moss unit uses, but almost every regulator IC on the market wants some capacitance near it. For example, the LM7810 and LM317 (which are also popular choices for VS replacement) datasheets both say explicitly "Ci is required when the regulator is located an appreciable distance from the power supply filter". (Note 30 in
https://www.fairchildsemi.com/datasheets/LM/LM7810.pdf )
Here's a photo I found of the Moss VS, being used to "prove" that no capacitor is required
If you don't want to "roll your own", you might just try adding a capacitor from the input terminal to ground. 0.33 uF should be fine.
PS, the lifetime on solid state components should be somewhere out beyond 100,000 hours, which is basically forever in automotive terms.