All finished now. Van was in for almost a week. Dropped the subframe and removed box. Said leak was from case seal and clutch guide tube. Also said slight weep from engine rear crankshaft seal - must have been slight as not aware of engine oil leaks. Wouldn't mind so much, but I paid previous garage to replace guide tube and crank seal just over a year ago while they were replacing clutch. Between clutch replacement and this latest extravaganza, the previous garage (who did the clutch) had replaced a driveshaft seal, which obviously didn't cure the leak. Partly my fault for letting it slide since then and living with a slight leak.
The crank seal and guide tube have been replaced again (assuming the original garage actually did do them). The box has been opened and examined then had a full reseal. There was play/wear in the shaft and bushing that links the cables and change mechanism on top of box and passes through casing into the box to swap the cogs - so shaft and bushes renewed. Internals inspected, no serious wear found.
Other incidentals were the broken coil spring that made a bid for freedom, couple of ball joint rubber covers and a CV boot. Luckily they found the clutch hadn't suffered much oil contamination - only misting. They were able to clean and reuse it - which I'm happy about as it only has 7,000 miles on it.
Together with the new genuine Fiat gear cables (an Ebay bargain) that I fitted myself last summer, the clutch and gearbox now drive like new and are bone dry underneath. I had thought that the notchiness going into second was worn syncro, but they said syncros were fine, Notchiness now gone, so must have been the play in the shaft and bushing that passes through box casing. Really pleased, but it did cost a bit. Glad I took it to gearbox specialist as they really knew their stuff and have good reputation. Wish I had got them to do the clutch a year ago.
This weekend it's time for me to change the oil and filter, then hopefully that's there's a good break before any more spending.
Thanks to all who replied with advice.