6 speed manual oil leak

So i have had a gear box oil leak since i have had the car. Seems previous owner had cleaned the car well before the inspection. it started off not a real concern, as i just kept it topped up with oil. the car is a c4 2002 cab with 67k miles. 6 speed manual Now at indy i have the gearbox out to do the clutch, flywheel, aos, and imsb. so thought would have him do this leak as well. Originally i was hoping for an input shaft seal needing replacement. What i have been told is actually the seal between the two halves is leaking and the gearbox needs to be spilt to replace it with a new seal. As this is a specialist job they want to send it to another garage to spilt and replace seal. its coming in at quite a high price as the specialist is busy. 1200pounds. so they are having a look around to see if anyone else can do it, Does anyone on here know if any repairers around london? My ignorance say spliting gearbox and replacing seal should be around 600 pounds. does anyone know the process and how much work is involved so i can weigh up the price. other option is to buy a refurb gearbox from ebay for 1400 pounds. Any advice on this? is it A) better to work with gearbox i have, replace the seal, as i know it operates well and just has a leak, + numbers will match to car. B) buy the refurb gearbox, and hope its been done right and not worry about matching numbers. Appreciate any thoughts on this

So just to clarify, you have been having to add gear oil to the transmission since you bought it? What gear oil have you been using?

I personally haven't been adding the oil, i have just had the mechanic top it up every 4 months or so. The porsche dealer topped it up the first time and the indys after that, assume they use the right oil. The gearbox operates fine, but now its out figure i should fix the leak. I looked through the service receipts and it seems it had the second gear syncro done 7 years ago. I ve only had the car 3 years or so,

Ok. It definitely sounds high but not ludicrously so. How much is the rest of the work running you?

its starting to get a little scary, but i guess in the big scheme of things isnt too bad, �800 for flywheel, clutch, aos - I supplied �600 labour for fitting above, and removing, fitting gearbox and installing imsb �600ish for the IMSB he wasnt entirely sure the cost, but LN single row pro ( i expect this to be closer to �1k �360 then there was the flex coupling from gearbox to shaft. Porsche sells it in one unit, so decided to go for entire package as labour to fit would be about the difference then we got into a few suspension parts and decided on new front shocks as have done the rear and needed a wheel alignment any way. another �1 k here so yes, not a cheap service and i guess the gearbox oil leak needs to be done. just seems extreme as the gearbox is out, and just a seal needs to be changed. is the process that difficult once its out of the car? looking at pictures it doesn't seem that hard.