In my admittedly limited experience steel threadless headsets are very prone to rusting, even when used with mudguards.
Three years ago I treated myself to an Audax Mk3. When I assembled the bike out of the box I was a bit surprised that the steerer was bare metal, and actually phoned Thorn to query this. They recommended taking it out once a year and keeping an eye on it. Well, after a few moderately wet rides I was horrified to see bright orange water trickling out of the bottom and over the mudguard. When I tried to take the fork out some of the spacers had been jammed by rust and it needed some taps with a mallet before I could shift it. It looked pretty terrible. I should have taken a photo, but set to work with a wire brush and wet-and-dry until I had cleaned it up. There was a bit of pitting but I assumed that as I am small and light the steerer was still strong enough for me. I treated it with Kurust and then Waxoyl before reassembling. I hope this has done the trick but I haven't used the bike in the wet since - in fact as I live in a wet climate I've hardly used it at all, which is pretty daft
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Recently I bought a s/h Raven Tour. It hadn't been used much but the first thing I did was take out the forks. I'm hoping the photos will appear below. Being 531, and with a trace of primer on it, the steerer is not so rusty, and it cleaned up nicely. The top and down tubes hadn't been blanked off (the Audax has some masking tape over the holes where they meet the head tube) so water had got in there and caused rust. I squirted some thinned Waxoyl down them, then when everything was dry covered the holes with some flexible tarry 'card' used for roof flashing repair - it is thin enough not to obstruct the steerer.
Water gets in between the spacers - also the stems are hollow, so water gets in via the handlebar clamp, runs down the stem and down the steerer into the headset bearings.... So in addition to putting Waxoyl on the steerer, I have also applied it to the ends of the spacer rings, and I have fitted some greased cork (from a bottle of Prosecco - hic!) into the stem just behind the clamp.
I think that is about all I can do. I think it is a major disadvantage of the Ahead design, at least if used with several spacers. My 1980s bike has been used regularly for over 25 years, all year round in all weathers. I occasionally dismantle it, and have NEVER seen a trace of rust on the steerer.
