The Michelin ProTek Max tube I installed two years ago developed a slow leak this year, which I eventually ascribed to the valve stem, because the sealant should plug any other leak.
Cutting it open reveals the perfectly good greenish-yellow sealant:
The sealant also carries black rubbery grit / shavings / dust, perhaps intended to jam inside larger gashes while the sealant coagulates and binds it together.
There’s a lot of rubber floating around in there:
Dismantling the Presta valve stem show the rubbery crud on and around the valve seal and seat:
Whenever I pumped up the tires, I finger-tightened the nut to ensure a good seal, as you do with all Presta valves. Obviously, finger-tight can’t handle that much crud between the sealing surfaces.
I’m sorry to say I was right about the leaky valve stem, because I think all the ProTek tubes will fail in exactly the same way.
The valve has small wrench flats making it easy to remove, so I can at least attempt to de-gunk them when they develop slow leaks.
Color me unimpressed.
