I will get flamed for this but here goes anyway. Usually a rebuild kit is not available for a R&P. First I would try "Lucas Power Steering Stop Leak". It won't hurt anything and may fix it. I have seen it work many times on R&P systems. It doesn't seem work on regular steering gear assembly tho.
Just remove as much fluid from the resevoir, put in the Lucas, and top up with clean fluid.

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84 500 SEL (307,xxx miles)