Taking the JT9d as a nice simple baseline engine
It used 7th stage hp compressor air for cooling and sealing. The no3 (situated at the hottest part of the engine) bearing also had 15th stage air to back up the 7th. If the labrinth seals got excessively worn 15th stage air could enter the (no3) bearing housing and possibly result in an internal fire in the bearing housing and the g/box.
The early JT9 (-3a and 7) had a breather pressure guage, this was eventually modded off in favour of a breather temp guage.