Yes, that's very common with older TLR's. Fortunately, a cheap and simple solution is to buy an old Polaroid ("one step" or one like it where the film comes out the front), take it apart, and use the nice little front surface mirror inside to replace your old dim mirror. Very simple, but you may need to cut off a little on the sides to make it fit properly. A glass cutter and a pair of pliers (I use needle nose pliers) takes care of that quickly.
It's an old Ed Romney trick, I did learn a few good tips from his books
Nathan