T25 gearbox 2nd to 3rd issue

[Matthew]

Hi there, I've owned my T25 1.9 petrol water cooled for the last 5 years. I replaced the 4 speed gearbox about 4 years ago with a recon box, Its been great up to now but its developed an issue when changing from 2nd to 3rd. There's a grinding noise when engaging 3rd gear. Although if I take her out of 2nd into neutral and wait a second or two before going into 3rd it is ok. All other gear changes are fine up and down. Just wondered if its a synro issue or hopefully its something less expensive i.e. linkage or oil??? I had a quick look under the box last night and there is wetness at bottom of box. Any advice gratefully received. Cheers

[Aidan]

So where is the oil leaking from ? Selector shaft seal or from behind the output flange ? It can be difficult to tell exactly so you may have to clean off with brake cleaner or the like and then drive and it will likely be more apparent where the weep is. I'm guessing it's just damp with oil film, no jew drop on the bottom of the box, not leaving a mark where it is parked ? You can always put a piece of cardboard underneath to get a witness mark when parked.
If leak is from selector shaft seal then I'd suspect a broken cup on the selector shaft which can lead to selector shaft rubbing against the mainshaft slightly limiting the shafts ability to rotate.
You need to check the selector shaft and cup and ball and boots to see no impediment externally.
Otherwise the advice would be drop the oil and see what the drain plug magnet has to tell us - if you find parts of a selector fork bearing shell or the balls from one then that would point at broken bearing and poorly supported and/or slightly baulked selector fork for 3rd 4th fork.
Have you contacted whoever did the rebuild ?

[Matthew]

Hi Aiden...many thanks for all that. So I've cleaned the box took her for a good run no leaks evident. I've just drained the oil and drain magnet is like a hedgehog iron fillings covering half of it. Is this a sign of gearbox rebuild or is it worth replacing oil? Also was wondering if clutch could be an issue but would guess I'd have an issue with all gear changes?