Just found out that my trusty M4 rear brake from 2006 has seized / non freely moving pistons. Which might explain why the last ride felt so much like hard work ….

Now, is it worth cleaning, perhaps putting new seals in etc ….
Or is it better to buy a new V4 that at least belongs to this decade?

2006, I think you’ve had your money’s worth. Celebrate it’s retirement by treating yourself to a new set.

My black and gold Mono M4 caliper is an 05-05 (May 2005 I guess) and works great – usually. Just changed the pads for some fresh uber sintered finned inserts, but still lacking. I’m going to drain and refill with minty fresh DOT 5.1, and I expect them to be great again.

They are a Frankenbrake – Tech master cylinder with Evo pistons and cams, silver/black M4 caliper on the rear.

I am fairly sure a set of phenolic pistons and seals would bring the OP’s caliper back to life.

A clean, new seals & a bleed will probably sort it.

Just looked up the rebuild on youtube ….
Hmmmm …. looks like a lot I could f*** up!

It’s dead easy. I’ve just got in from the last post after bleeding the Reverb Stealth and F&R M4’s. Nothing blew up. Which was nice.

Rebuilds a bit fiddly but new pistons(worth going phenolic), seals and it so from brand new again, I think hope do a complete rebuild for 40 quid an end lever and calliper, which including pads of a bargain, but obvs you could get a set of series for that process

As Kimbers says send it back for a rebuild or buy a new brake. They have a very hard life and 10+ years is a great innings with no major issues.

Mine were the same after about 8 years of use & abuse. They were siezed and sticking. Popped thr pistons out, cleaned and put them back, same seals etc and they work perfectly.
Treated it to a new set of pads and they’re as good as new.
Certainly not worth spending on a new set until you’ve at least tried to service them.

My 2009 M4s were feeling ropey, sent them back to Hope for a full rebuild. Sent them Tuesday, had them back by Friday good as new. Think it was about £90.
Probably wouldn’t bother trying to service them myself for that price.

I’d rebuild them. I’ve done it a couple of ours over the years. Some of them will be of similar age to yours

Rebuild them. That’s the beauty of Hope brakes. Do it yourself, it will help with your understanding of exactly how they work. If you mess it up, then send them to Hope for an overhaul.

Yep, go for the rebuild. I’m about to do rebuild No 2 on my 05 callipers but the bore cap has sustained a hit and won’t unscrew….
Time to practice those gynaecological skills of replacing all the bits without undoing the bore caps….