[newday777]

80-81 are 1 piston calipers.
82 uses both calipers to the front master cylinder.
83 is linked brakes, right front to rear and it is a smaller diameter piston than the left caliper, 25mm vs 32mm. I don't remember, and cannot look it up as I'm away from my computer doing this on my phone if 82 & 83 left front are the same caliper. I think the pistons are different lengths but same diameter.
Many ebayers are just parts strippers and don't know the differences and assume that what they put in that will fit is correct when in fact, as with these brakes, there are many changes in each year. It is buyer beware.

Pull your caliper apart and get a rebuild kit, clean it out of the gunk in the seal grooves, clean the pistons or replace them if pitted badly.

 

[newday777]

Rebuild is not hard, just use the master to pop out the pistons before you disconnect the hose. I use a block of thin plywood or an old brake "pad as a stop to ensure both pistons move out before popping one out completely as if one is stuck you need to put a shim to hold the other in place to use the hydrolic pressure to release the stuck piston. Keep your fingers away!

If you haven't been flushing the systems yearly since new or rebuild, you will need to rebuild calipers and master cylinders as the gunk builds up in 2 years time, sticking can be gunk in seal grooves and or the return port plugged in the master cyl.