Best replacement caliper.....

[darrsi]

Darrsi, no and yes respectively, one of the first things I did when I went back to the 600 was to search for a replacement rear caliper. It's also the sensitivity of these calipers that is important; I always felt like the standard rear setup had wooden brake pads & I could not sense when it was about to lock up. And that was despite still-moving pistons. The 43mm piston rear calipers are surprisingly easy to control.
For the cost of new replacement Yamaha seals you can have an alternative caliper, so for me it was mandatory not optional. And if you don't observe a very strict cleaning regime a couple of times per year, the original caliper seizes up.... whereas I can be a lot lazier & overhaul mine every 18 months or so

I give my rear caliper a good toothbrushing with brake cleaner, then regrease the pistons at least 3 times a year, just for the sake of it, but it's a quick enough job, you're only looking at 30 minutes per go.
Seems to keep it in good nick though so it's obviously worth doing anyway.