Castor block/steering spindle bind

[DaveG28]

Having a mare trying to get my castor blocks/steering spindles built on the 502, sameparts as the 511/db01, basically the left binds when you turn right, and the right hand side binds when you turn left!!

Ironically I helped Rich D with this in the summer, but now can't do it myself, is there some trick to avoiding the binding problem??