What's a front seal (input shaft) worth to do on an ED 4spd auto.
I think mine leaks, cause there is a nice 3 or 4 drops of red oil sitting under it, but it could also be my dads car.
How hard are they to do, as i'm also considering doing it myself if it's relatively simple.

There cheap to buy your auto parts store should sell em. I did mine back when I fitted the gearbox, got it from Repco.
It'd be a C*** to do once the box is in, as I think your' have to remove it, to get there, as the torque coverter and that would have to come out - I think.
If you've got the time you'll save a fair bit of money, but it's a b**ch of a job and not the easiest without the right equipment (i.e. hoist and tranny jack - wish I had them when I did it!).