Just working backwards chap, if you have checked the calipers are not sticking , tyres are good etc then the possible route causes are getting less rapidly.
you have replaced some worn parts too.
Normally the next thing would be an alignment issue, as its not a problem that is restricted to under braking conditions as you say it's there all most all the time.
to eliminate another possible factor, swap the front wheels round and see if there is any change, if not that deffo eliminates tyres.
so you still looking possibly at alignment issues maybe as a result of the subframe movement.
could be the rack , but there is a strong case for mis alignment or similar problem as your getting it all the time and that's has a common connection to the fact that the problem arose around the time you were doing that work on the car in that area.
just looking at the wider picture chap really, something changed to the car's front end on or about the time you said you did the gearbox work, cant help getting the feeling the two are connected but maybe wrong as i'm not an expert, just giving you some extra ideas to work with.
Did you disconnect the front drive shafts when you did the gearbox work chap, just possibly another area to look at aswell as it maybe relavant.
rob
