I've had mine mounted for nearly 3 years now, on a T-piece on a T-piece(yep, two! .. as I also have a oil temp sensor too)
So far no problems with vibes, nor operation ... approx 60+K klms now.
To begin with I used O-rings at the end of the threaded t pieces, and they used to leak after a while.
Then used a very small amount of plumbers tape(gas type) making sure to leave some bare thread to allow earthing.
That also leaked.
Finally went to a plumbing shop and got some thread sealer goop, brand 'LOXEAL' no idea on if it's a specific type or what, just says 'engineering adhesive' and 58.11 and what looks like a W(but could also be a logo).
Brilliant stuff! 
I've used it on all manner of stuff now, allows earthing, but seals better than anything else I've ever tried(incl loctite).
Last time I used it was on my compressor fittings, all of them, replaced with new bits, and prior when we used plumbers tape on it, it'd always loose pressure over a day.
Now hold 110psi for at least a couple, and more than 60psi for a couple of weeks(out in the weather too!).
Comes in a silver squeeze tube with a white cap.
Needs some effort to come off, so kind'a acts like a thread lock too. When you release the sealed item, the remaining goop is semi hard/semi soft, and crumbles off easily to allow refitment again.
Highly recommended .. and my experience so far with VDO sensors(both pressure and temp) on t-pieces has been fine.
FYI: t-pieces I used are the common aluminium things easily found at various places(speed shops/ebay/etc).
Arthur.
All these discos are giving me a heart attack!
'99 D1 300Tdi Auto ( now sold :( )
'03 D2 Td5 Auto
'03 D2a Td5 Auto
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