Thanks all. In retrospect dropping the engine down far enough was so easy I don't want to hold up getting her back on the road too much. It turned out one of the breather pipes had worked loose from the hose joining it to the top of the tank.
I will be:
- cavity waxing around the petrol tank
- replacing ALL the breather hoses (question: why the two long straight 7mm pipes above the tank with a short hose at both ends? I intend to replace each of the two pipes with a long piece of hose to reduce the number of joins and therefore potential leak points)
- putting decent jubilee clips on every breather hose connection
- actually connecting the two breather pipes that are currently open at the rear of the engine bay to a T-piece and thence to the air cleaner
- sound deadening behind the firewall
- adding soundproofing above the holey-sheet in the engine bay
- replacing 4 very rusty bolts holding up rear support bar
I've ordered all the hoses, T-piece, reducer, elbow, clips etc. from advancedfluidsolutions.co.uk - very comprehensive and much more reasonable than VW suppliers.
Wish me luck
Dan