Len3.8, I assume there must be a reason why you want to repair or replace this amp with one and the same vs. buying another amplifier.
I just did a search on Google to see if I could dig up info on the MC120 amplifier. I found a thread where a guy had
9 of them in a box as of September of last year. He might still have them.
http://forum.e46fanatics.com/showthread.php?p=1928306#post1928306
From what I could gather it's a 4x30 amp that's over 10 years old. It was made by the old Soundstream which was a better company back then. A quality amp in the 4x50 range can be had starting about $150. Used even a lot less. The new ones are made by a much lower end company called Power Acoustik since Soundstream was bought out and really isn't in the same class of product as it used ot be.