I'm on my 7th GL1800 right now, I replace them at 30,000miles or 2 years old, whichever comes first.
I've had 2 bikes out of the 7 with a front wheel wobble that started at around 600miles.
The front wheel felt as though it might be loose at approx 30-40mph.
Eventually, both bikes were completely cured by fitting All Balls Tapered steering head bearings.
I also have a pal with a 2008 GL1800 who, because the bike was new, took it back to the dealer for the very same problem - a wobbly front wheel feel at around 20-40mph.
They fitted a new front tyre but the wobble came back around 900miles later.
He asked me if I would fit him All Balls Tapers so I did - it cured his problem too, no more wobbly wheel feel - he's really pleased with the bike now.
Another pal asked me to check his because he was getting the wobbly front wheel feel BUT the first thing I did was check his tyre pressures and tyre wear. The rear tyre pressure was 32 and the front was 28 - the rear tyre was wearing flat so I increased his tyres to 39fr 41rr and he said it felt "alot better" - so much so that he doesnt want the head bearings changing
Make sure you always check your tyre pressures very regularly and keep them correctly inflated.
Also, keep an eye on the rear tyre for flatting as this could cause the wobbly front wheel feel too.
Just for your info - when I stripped these bikes down to remove the bearings and fit tapers I checked the Torque settings and on ALL 3 bikes the torque was less than stated in the Honda workshop manual - the locking nut, (same on all 3 bikes), wasnt tightened at all, it was finger loose and wasnt doing anything at all to stop the main nut from working loose.
I'm not a motorcycle engineer or a tyre specialist, I'm just reporting my own experiences.