CB500T transmission problem.

I have a '75 CB500T I have been getting back on the road for the lost year... just when I thought I was ready to ride I find a transmission problem.

It slips in 2nd gear (only in 2nd) under any level or power, it holds when down shifting to slow but slips if you forget and try to accelerate in 2nd.

I have never worked on on of these transmissions. any one have any ideas? Is it hard to take the gear set out and replace the bad gears?

Thanks, Howard