No power steering - right turns?

[will66]

I have an '83 300SD with 210k miles, and recently it has become difficult to turn the steering wheel to the right. Left turns are fine, but right turns feel as if there is no power assist.

First thing I did was change the PS filter and fluid, but the difficult right turns persist.

I have searched the forum, but I could not find a similar problem previously discussed.

I am not familiar with the internal workings of the pump, or the steering box, but I am not afraid to pull them apart...with the proper guidance.

Any suggestions are appreciated.

Thanks.