I still can't see how it can be rotated by those influences you describe. Do you have mischievous mice living under your bonnet?
But if you really want to chain it down, get some black self amalgamating electrical tape, stretch it as instructed and wrap several turns neatly around the cap and body junction. If you need to adjust it later it can be removed easily, but it will immobilize it for keeps until then.
(Late edit) Aha! I just had a thought. The small vacuum hose fitting at the top is a swivel fitting. Might be a stupid question, but are you really sure it is the cap that is turning, and not just the swivel fitting adjusting its position according to mild lateral tension on the vacuum hose? That could easily give the impression of the entire cap rotating.
Last edited by Doug_MPS6; 19-01-2011 at 05:37 PM.
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