So I have a really worn rubber boot that surrounds the pushrod going into the master cylinder on my Formula R1 rear brake.

After bleeding both brakes today, I can hear a squishing sound and see a tiny bit of fluid oozing around the boot. It's not "leaking" per se, but it doesn't look all that healthy either (partially split around one side and a bit loose looking). The front lever's boot is more uniform and snug-looking and the lever makes more or less the expected sound when cycling the lever.

This was my first time bleeding my year old brakes and I'm wondering if I just maybe overfilled or pressurized the system a bit and this squishiness is just making itself apparent at one of the weaker points in the system....and if that's the case, if this is a sign that I could end up blowing out the whole cylinder or losing pressure when braking hard... That's my worst case scenario thinking, where I'm plunging down one of the massive Alpine descents I so love and I lose one of my brakes completely.

It appears if I want to replace the boot I need to buy an entirely new lever from Formula for nearly $100 and the older (2010 lever) isn't even available from what I can find.

Are my concerns possibly misplaced and the squishiness stems from the master cylinder under the boot?

Any thoughts/opinions would be really helpful.