1983 KZ750 L3. Really Struggling For Brakes

As long as the old seal is not broken or has cracks in it I always reuse them. Just clean them up and reinstall. I stay away from the aftermarket one's as the ones I've used always leak. I've cleaned up and reused OEM seals that came out of 40 year old calipers and never had issues.

Clean brake parts and seals only in or with fresh break fluid. All other liquids like breake cleaner or thinner fluids will destoy the seals.
Break fluid is no oil, it´s a glykol basic liquid (DOT3, DOT4,DOT5.1). DOT 5.0 is a Silicon Basis liquid and don´t mix with other DOT brake fluids.!!!