Deere 410C sucking air into brakes

I have a 410C that has a weird issue that I've not been able to track down the cause of.

Brakes work perfectly fine, no leakdown, etc. Master cylinder was recently rebuilt and fully tested OK. If the machine sits for 2-3 days, AND the temperature changes significantly during that time, the brakes get air inside of them on both sides.

I know they are sucking air into the brake ring area as just a single pump of bleeding fixes the problem. The longer the machine sits, the more air in...

Deere 410C sucking air into brakes

Deere 410C sucking air into brakes