Got an old pair of xt disc brakes over 10 years old. Performance isn't great after a bleed and cleaning the rotors. Think the rotors could be contaminated as squeal like mad. It is worth buying some new rotors or is it likely the brakes / deals have had it being 10 years old? Haven't had loads of use over the last 10 years due to road riding.
Assuming that the seals aren't leaking, they should be fine. If the rotors aren't badly worn, I would try cleaning them thoroughly with hot soapy water then lightly sanding them. Then fit new pads and bed in.
Tried the light sanding and disc brake cleaner but started squealing again on the 2nd ride and getting worse.
Leaking seals. Brakes are scrap
Shimano rotors new are 1.8mm thick, Shimano advise to replace them at 1.5mm, might be worth checking.
A degrease of the rotors with IPA / disc cleaner will sort any contamination issues, add in some new pads too, but at 10 years old the caliper seals might be the culprit.
It does sound like leaking caliper seals. If the levers and hoses are still in good nick, maybe just replace the calipers.
Pads. Far more likely to be goosed than the rotors, worth trying before binning.
There is little point cleaning rotors if you don't replace the pads at the same time. Most of the contamination from the rotors quickly gets absorbed by the pads.
New brakes.
10 years on a set of shimano's must be a record. Are you sure they work at all 😆 Go on, treat yourself, you deserve new brakes once in ten years.