Well, are you ?

Sam 
My RD400 is about the most fun I've had on a bike. I don't ride it much these days since I know its life-span is short and best left to short, fun, trips.
I have fond recollections of my R5 and RD350 as well.
They were some of the most flickable canyon carvers back in the day.
And their powerband was very well suited for tight technical curvy areas in the mountains.
I would like to own another, maybe a later water pumper variant?
But the prices that these are commanding these days is hard to justify.
Why dont you try to stockpile motor parts for it on ebay?
There are still some out there, not cheap tho....
(and some used bits of questionable quality)