I have a '72 Mach 1 which at some point in it's life had the
engine(and perhaps transmission) replaced with a 302. I noticed some
dripping under the car, so when I went under I saw drops of oil where
the driveshaft goes into the transmission. The oilpan seems to be dry
on the outside, so I suspect the transmission is leaking. I bought
some 80-90w oil and put almost a quart in the transmission before it
got full. Is this transmission worth fixing? It seems to work,
although it's a pain to get in and out of reverse. I don't really have
many tools beyond a socket set right now; and I'm assuming I'd need to
pull the engine to get the transmission out?  Would I be better served
to try to find a used transmission and just swap them out?

One other thing, I noticed that when the engine revs up over 3000 I
hear a screeching sound. Below 3000rpm I don't notice it. Doesn't
matter what gear I'm in, it does it even with the clutch in. Could it
be just a belt? Water pump? Or something worse?

Thanks,
    Neil