I would check retrobike.co.uk

If any website has a pdf, it would be there. I sold a bunch of AMP stuff awhile ago, manual included. It's not super complicated, but you need a very large cotter press looking tool and some other bits to even attempt it. You also need a set of new bushings to replace the old ones.

Pretty much the only thing you can do without replacing parts is refill the oil in the tiny damper. If I recall that takes standard ATF fluid you can buy at an auto parts store.

Edit: Found an old picture of the tool kit