[anotherboffin]

Maybe OP is “stuck” with shitty hydraulics from a lesser-known vendor for which it’s difficult to get the parts? I’d say they look into the cost of getting the whole system replaced, my Shimano low-ish end hydraulics have worked fine for years and as you’ve mentioned, parts are easy to get.

[ggm]

Tektro HD-M275 front and rear. When I go online, its ali, ebay and grey market suppliers mostly, not a heap of returns from recognisable Australian bike shops.

Maybe its my bad timing, buying a 2nd had bike when it was end-of-life for one model of brake, and now it needs work, people have moved onto the next 'best thing' and I am behind "can't get the parts"

(I know one respondent disagrees and says they are both easy to fix, and easy to get. I am just reporting both what I was told and what I find when I look. "easy" is very contextually defined in both cases. It would be very easy for me to confuse myself, order the wrong bits, or manage to dismantle but never re-mantle things.)

[midoridensha]

This is an addendum to my other reply to you. I only briefly googled for this model, but my guess is that it's an older model. It should be possible to find a newer product (either from Tektro or better yet Shimano, which uses the same kind of mineral oil as brake fluid so you can probably reuse your lever if you want, if it's the caliper that needs replacement) which is compatible with this system's mounts. You'd be better off doing that than trying to get an exact replacement: newer designs are usually better anyway, plus they're frequently cheaper since they're current production.