Thanks for your reply I'm quite handy do I just add normal injector cleaner to the petrol to clean them .
The lpg system has the donut tank I the boot the vaporiser is the square looking one with a bolt in each corner holding it together . I see there are kits online to renew the seals . There is a inline canastier about the size of a dd battery that's yellow gold in colour . And yes it comes on ok when the engine is hotter , I flushed the raditor as I know the pipe heat the vapouriser .will try get some pics
I've used this to clean them http://www.lpgshop.co.uk/ic12-injector-cleaner-and-lubricant-100ml/
You need to put it in upstream of the GAS injectors - Though with it being Landi it may not be omegas it may be the other system they do with the two motors. Some photos of the front end will help with that. If you follow the hose running to the canister bit (which i would assume is your vapour filter) then if you have injectors you should see them. It may run into a different assembly, if your not sure then get photos.
Theres no reason as yet to suspect the seals - generally it will leak gas somewhere it isn't wanted (either into the coolant, out to the atmosphere, or up though the vacuum line into the inlet mainfold) - in any of these states you will either smell it leaking, or find very poor running. You don't have that, so would suggest leaving the vapouriser alone at this stage.