The WTB Momentum headset is one of the best 'Britain friendly' products that I have used in Aeons. Almost nothing seems to be able to stop water and mud ingress into the bottom headset race, so the ability to replenish the grease from the outside is a godsend for muddy funsters like myself.
My previous headset was an FSA with cartridge bearings, and the lower race bearings would go rusty after only 6 months, even with an old inner tube gaiter fitted. Now I ride without any type of 'headseal' or gaiter, and give the races a squirt of grease every 2 or 3 rides. The scary thing about using this headset is that if you regrease it after a really wet ride, water spits out from behind the 'O' rings!
That said, the seals ain't that bad either. I've just returned from 800 miles of road touring in Scandinavia, including some appalling rain, and there was no water damage to the headset.
At £30 to £40 it is excellent value for money, and should last a few years. It is just a shame that the Paradigm model isn't available in the UK (with replaceable cartridge bearings) so you could fit new bearings when the races eventually wear out, without having to resort to the big hammer.
Also remember to fit the headset with the greaseports in an accessible position (sorry about mentioning that Ozone!).

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