Trying to find a water protect distributor will be very difficult, and one in good condition even more.
There are distributors for sale for the P engine, since it was used extensively on fork lifts. I personally think they will be better performing than the water protect type, since the water protect dates to 60s and the other was developed during the 70s. My guess is that they improved somehow. Mine never had the water protect. I can't swim

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In this thread you'll find more information and links:
http://www.60patrol.com/forum/viewtopic ... 57&p=42765
At the end it all depends on whether you want to ford deeper streams or not.