Juddering steering!

New Bridgestones 300 miles ago and its juddering at 90+mph. Took it back to tyre fitter and they removed wheel re-balanced it and I was there to see the machine balance it again. It was already ok but we removed and re-applied a new weight anyway. Went for ride and still juddering. Pressures are ok and I tried harder and softer pressures.
Apparently I may need the front bearings doing, does this sound like a fair assumption after whats happening?
Thing is I sold the bike and the man wants to collect next week.
I have told him its juddering and said I would sort it.
Now its not the balancing have I landed myself in it or should I do the right thing and pull out the sale?

All this and I could have come to the AR because the bike is still mine, GRRRR............

[Red Herring]

When iou had the front wheel out for balancing did you feel the bearings yourself? The wheel bearings are dead cheap really and easy to fit, worth doing for just the peace of mind.

yep bearings cost about £15 for the 2 if that. Done the rear wheel bearings + cush drive one cost me £25 for all 3 and a can of chain lube.

Do the bearings yourself or if not take the front wheel off and take to a garage with the bearings yourself and they will charge 1 hours labour tops which for a backstreet garage will be £40 max.