Tail wheel shimmy

[GMKman]

Not sure if this the problem you're having but when I owned a Glastar tail dragger, the tail wheel would shimmy when the springs started to "sag" hence changing the caster angle of the swivel bearing. A wedge shim or re-arching the spring would fix it. That's assuming the bolts are tight and the bearings are not bad.
I hope that helps.
Brad.