244 1989 leaking transmission fluid

[carl]

I have a 1989 244 Wageon with manual transmission. It has a slow leak that the mechanic has identified as transmission fluid. The mechanic said that it might be the seal or gasket. Can I just 'top up' the transmission fluid myself? (Where do it put it?) Is the wageon worth fixing if the transmission goes? Otherwise, the car runs well, except it really whines in first, second, and third gear sometimes.