Foam means air is getting into the system, could be low on fluid.
I'd replace whatever is leaking. If you replace the steering box, get one for a '99 Durango 4wd as it is a heavier duty unit that bolts right in. I got mine for $75 from
www.car-part.com .
As for removing the pitman arm, if it comes down to that, tighten the puller on real good. Then smack the side of the pitman arm where the shaft goes through with a 3lb sledge. Tighten, whack, repeat. They generally pop right off.