What the hell?

What the hell? I went to change the WR-R steering head bearings, and found a dust bowl inside the head. Pic taken AFTER I'd wiped half the dirt out! You're looking from the top of the steering head down towards the bottom bearing race. The seals are absolutely fine, plenty of grease still on them, no dirt in the top bearing at all. Odd.

So where is this stuff coming from? This bike keeps coming up with surprises I'd rather not have. No awards for guessing why the bottom bearing is prematurely shot.

The frames hollow (you can see it in your pic) with vent holes in it, dust will come in but I'd never expect that much in there.

What about some spray foam down the frame to seal off the steering neck? So where is the hole letting the dust in? Dust and sand =No good for bearings.

Yes, I reckon you're on the right track. I have an old air filter oiled and lined up to be wedged into place.

I realise the frame is hollow with breather holes, but I never expected dirt up into the steering head! This opens up a whole can of worms form all riders re steering head. Dump it in a creek? Water in the bearings. And so on.

How was the bearing and race? Any signs of rust? Think I would seal mine off!

The bottom bearing is, as you'd expect, totally stuffed. No rust though, as the bike has never been wet. Not even washed. What's a bit of dust?

Seriously, I just blow the dust off occasionally, especially the radiator core. If one off my bikes gets muddy though, I get all paranoid and wash it immediately. I hate mud