It won't be the seals in the caliper it will be more likely a warped disc. I have only had 2 instances when the brakes have dragged on my 84 CR's and one was the piston kit in the master cylinder (this will stop the piston from retracting and is a common cause) and if you say you have removed the master cylinder and they are still dragging it will be most likely a warped disc (they turn themselves inside out and curve one way with age, specially if worn) take the disc off and lay it flat on a desk to check this, flip it over and measure the distance of both to the desk to check this. It is hard to pick by eye on the bike and as it is not bend it will not drag as such (like a tight spot) but will be firm as you spin the wheel all round.
The seals in the caliper themselves are pretty bullet proof (I have found anyway) they have a very basic function and are only really a problem if they are leaking.
As usual Only my 2 bobs worth and I have been wrong before but have had several of these bikes as vintage bikes and this is the problems I have incurred.
Shane
