Hiya, try getting hold of Vosper Thornycroft, Portsmouth UK they made the drive many years ago and I believe they still stock certain parts. Phone no: +44 (0) 1705 383311.
I have a PP65 jet drive, i'm not sure what differences the 65 and 90 have. but i currently stripped down my jet drive and it's a very simple set up.
I know there is a pp65 parts guide on the internet and basic information on it.
Hope you sort your issues out with the jet drive
cheers
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