Well after looking around for a few months, I have decided (after a painful trip back from Brands Hatch) to book the car in to have the gearbox checked over.
Only gear causing me issues is 3rd (above 4000rpm) where it just doesn't go...Anything below that, its a smooth as silk. The car was bought with this issue, and so its nothing I have done. Ive also given the gearbox 3x fluid changes in the 2.5yrs ive owned it just to limit any potential damage as best I can.
Tried a few recommendations and costs were quite high but all within £500 of each other.
Settled on these guys
www.rmperformance.co.uk - had some good reviews, and they seemed to know there stuff, suggesting whilst the 3rd gear was being sorted, I opt to the have the 4th, 5th, and 6th baulk rings upgraded to the carbon rings, as per Subaru did from the factory with the later 6-speed boxes.
Removal and refit costs were reasonable (less than £300) and so its all booked in for the 1st July.
They have given me a budget worst case cost for just the third gear synchro, including the upgraded baulk rings and its competitive. (based on every component needing replacing)
Obviously these things can open up a can of worms, but as with everything else on the car, I want the basics to be solid and sorted, so it needs to be done.
Shouldn't need the clutch and flywheel replaced as these were only done 1.5 years ago (Exedy Pink Box + Lightened Flywheel) but they will check these for wear also...
They will also check over all the other gears for signs of problems before they happen and advise any costs prior to going forward. Or they can just put the box back together if costs get silly
Also put in an email to Alyn for some prices on a few other upgrade parts for other areas of the car and so might have some more updates to follow shortly...
Ryan