Have you given Gast a call or email? I looked but the information I found was confusing.

I did see that Marathon was the Motor not necessarily the compressor. Your motor is obsolete, but note said give Marathion a call for replacement? But then is it time for the old compressor to be rebuilt? How much do you want to tinker? I would find a rebuild kit for the compressor before I bought a new motor. Probably not. Another rotary vane ? Rotary vanes appear to be easy rebuilds if you can find a kit for your old compressor. I like the look of the Gast & that it is rotary vane. I think I could easily do all the maintence on a Gast. I saw some new Gasts on eBay for less than $400 but I am not sure they are what you need.

Good Luck!