It is possible that old , perished and unevenly or badly worn tyres , especially the front could cause a bit of a wobble on the front end . I had the same problem a year ago and the front tyre was definitely worn and perished .I put a new set of tyres on , but at the same time had the forks off to fit gaiters , fitted new handlebars and fairly hefty bar weights, the problem disappeared but as I'd done a few alterations I couldn't really isolate the real reason it was happening . To be honest I reckon half the issues we get with bikes are down to voodoo !
If you have twin discs on the front it might be worth considering sticky caliper pistons .
