Sorry I got ‘warranty work’ confused with servicing. What I meant was it’s this idea that all servicing must be done by the dealer that sold it to you else “warranty is void”.
That’s the trouble when you start quoting English law especially concerning Italian bikes! 
UPDATE:
Got the bike back the weekend before last… and it was still leaking after a ride out the next day.
I did check the amount of oil they had put in the bevel box after their first attempt - it was too much, coming out of the check plug at the back of the box. Only by about 50mls - I’m not sure that is what has led to it continuing to leak.
Anyway, the bike goes back to Doble’s this evening to attempt a fix for the second time - this time replacing the inner oil seal and the gaskets.
We’ll see whether it works…
As an aside, and no help whilst you are under warranty - I have Nigel at NBS sort my drive boxes when they get leaky. I just drain the oil, pull them off, put them in big padded box and post them off. Postage is around £30 inc. a good chunk of insurance.
Note - Be careful if you are thinking of using Hermes for cheaper postage. I think they have a no auto parts policy.
I’ve now been told that the “dust seal” on the rear wheel needs replacing and do I want it done - meaning the bike won’t be ready till tomorrow evening instead if I do want it fixed.
Does anyone know what they’re referring to…?? Should I bother, or just wait till the next service to get it fixed by a Guzzi specialist?
Ah, just spoken to them - they’re referring to a dust seal on the axle spindle. I can get that fixed myself sometime…
Thanks - that is useful advice.
Jim
Can’t you find someone else who better knows what they’re doing? Like I said earlier so long as it’s a VAT registered workshop / mechanic, warranty won’t be voided.
Is that right tho, 500 cc in the FD? 
(Tonti big blocks only 250 cc. I 'member cos I would get 2 x 1 litre bottles, put 1+1/2 into the gearbox and the remander into the FD.)
Got the bike back this morning.
It looks like it’s fixed. It turned out to be one of the main gaskets of the gasket-spacer-gasket sandwich between the two main parts of the bevel box housing.
It’s 170mls (170cc) of oil in the bevel box, and they appeared to have over-filled it by around 50mls (50cc).
Anyway, all good now, except that they spotted that the dust seal on the left hand side of the rear axle is perishing and will need replacement. They even gave me the part for free to be fitted when I get round to it!
Jim
Fairy nuff!
On the back of the above posts, I have a 1982 V50 Monza, which has started to leak from the rear drive. This first appeared after I checked the oil level! It first appeared in the wheel rim when the bike was on the side stand overnight & I find oil on the drive side of the brake disc & yesterday after a ride out there was oil across the tyre. I note from the workshop manual that to replace the gasket(s) a couple of specialist tools are required? Living in Cornwall & a long way from a main dealer, I wonder if anyone has attempted this job at home or knows of anyone who works on Guzzi’s in Cornwall?
heard so many storys of guzzi dealers overfilling bevel box,how hard is it for them to do it properly?