I see lots of questions about hydraulic brake-specific maintenance. I.e. related to the hydraulic system itself, not the pad/rotor interface. (For this question let's ignore the latter since that's generally applicable to mech disk brakes as well)
Most of these questions are spurred by some specific issue: mushy levers, leaking oil, unsuccessful bleeds, etc.
That got me wondering, assuming your hydraulic brakes seem to be working perfectly, should you ever do any kind of preventative or regular maintenance on the hydraulic system? E.g. should a brake bleed or replacing seals or anything else be done every X number of km/seasons/years even when everything is working fine?
As a specific example, I've got a fat bike that's approaching 7 years old. Being a fat bike, it's still low mileage - around 700km. It's got SRAM Level hydraulic brakes. I've never had any issues with the hydraulic aspect of the system: levers are still firm and apply lots of force to the pads with good modulation and no mushiness. Should I leave well enough alone until that changes? Or should I do some preventative maintenance now?
I guess the motivation for this question is wondering if the hydraulic system can suddenly fail catastrophically with no warning if not maintained. Or do all common failure modes telegraph failure somehow, e.g. with slowly decreasing brake effectiveness?