Disc Brake Caliper Piston - Lube or Not?
 

On a BMW motorcycle.
Cleaning the calipers and replacing the pads...should I lube the pistons (pucks) or not?
If so, what to use.

Thanks. :)

Been reading online and some say that silicone will swell the seals...others say no. What say?

The answer is from your inspection. Are the calipers working fine, and no cracks in the rubber dust seals? If they would keep working fine with just a cleaning and brushing off of the brake pad dust, then why take them apart?

Not taking them apart...but two of the four pucks don't move as quickly and smoothly as the other two. They're clean but just a little sluggish when I pump the lever...so thought I ought to lube them a bit. No?

No lube. The brakes work by deflecting the seals. The only time they actually slide is when the pads have worn enough that they need to self-adjust.

I wouldn't want to mix anything into my brake fluid. Silicone fluid is know to be very spongy since it dissolves air much more than normal DOT4.

Ultimately, I'd consult the repair manual.

We used to recommend PBR rubber grease. Non deforming. You can only buy it in huge tubs now though... So Alcon makes these small containers specifically for brake seals and pistons: https://alconkits.com/tools-and-supplies/tools/alcon-caliper-grease-replaces-pbr-rubber-grease-detail