Bob,
It occurred to me that the other issue could be that the grease has simply gotten old and is "caked" in there such that you can't force new grease in.

I suspect this is the reason Volvo instructs us to relube these fittings every 750 miles - not because the grease would go "bad" (stop protecting the joints), or run out in that amount of time, but because it is easier to force new grease in before the old stuff has oxidized into a solid unmoveable mass.

What type of grease is in the fittings now, if you know? If Mobil 1 (or any other lithium complex synthetic grease), it will be a lot harder to dissolve than say a petroleum "soap" grease.

Petroleum grease is just that: a product of petroleum refining and it will dissolve in naptha, xylene, or my favorite, 3M Adhesive and Wax remover (http://www.autobodytoolmart.com/p-11319-4520-3m-adhesive-wax-remover-03618.aspx)

Also see:
http://books.google.com/books?id=L3NKAAAAMAAJ&pg=PA221&lpg=PA221&dq=petroleum+grease&source=web&ots=fv9BHr989D&sig=rAHdh6v8XR6PqcQhOJ-EnRxzhjM

The synthetic greases may be "better" because they resist "water wash out" (don't dissolve in water) but this also means they are darn hard to dissolve in anything. Believe it or not, I spent a better part of a year of my career trying to dissolve a synthetic "sodium complex" (synthetic) grease, without success! I tried many many solvents... (good thing it all pays the same..)

The point of all this is, if the grease is caked in there, you could try pushing a solvent through the fittings/joints to loosen it. You could also also try a heat gun (dryer) to see if this lowered the viscosity of the grease enough to get it to flow enough that you can push new good stuff in (grease is ~80% oil). The thing to keep in mind is that any solvent you pick better be compatible with those rubber/plastic seals - if they're polyurethane, no problem. If vinyl, solvents could dissolve them.

If all of this fails, you've waited too long to relube your control arms, tie rod ends etc and if its really bothering you, you'll have to dismantle everything and relube the hard way - by wiping out the old stale grease, reassembling, and trying again.

:(

Let me know how you resolve it in either case.

belinda