SRAM eTap AXS Service Manual page 14

Spray isopropyl alcohol inside each piston bore, the inside and the
10
outside of the caliper, and all of the removed parts and clean them with
a shop towel.
Do not use mineral oil or DOT 5 fluid. If the brake system has
been contaminated with mineral oil or DOT 5 fluid, the braking
system (e.g. the brake-shift lever, caliper, and hose) will need to be
replaced.
For the best braking performance, use only SRAM DOT 5.1 fluid. If
SRAM fluid is not available, use only DOT 5.1 fluid or 4 fluid.
NOTI CE
14
Caliper Piston Removal