I have had my rm 203 for 4-5 years now. I think it is a nice little cheap amp. I would do as suggested and buy a new one and save yourself the headache of buying somebody else's problem.
Not sure about what you can do about your antenna situation, but I live in a townhouse and I mounted a vertical dipole (two fiberglass antennas) on a painter's pole that I can raise to 12 '. With the 4' antennas that makes it about 16' to the tip.
I can talk locally on sideband to real base stations about 60 miles away to the west if me and about 35 miles elsewhere. When skip is decent I have made many dx contacts with my old Uniden Grant, the RM 203 and my crappy little antenna.
