Update
So on Sunday I unscrewed the allen topped adjuster which is attached to a brass tube that has the two rubber o-rings. The tube was connected to a diverter under the sink that has these funky press connectors. After a bit of struggle (you push the pipe in then press the plastic connector to release) I got it out. Visit to HD resulted in no suitable o-ring replacements.
Here's the assembly with twisted off allen adjuster
Needing the sink later that night I reinstalled the assembly and ended up twisting the allen adjuster off the pipe...DOH!. It was really corroded where the water passage holes were and just gave up when I applied a bit too much force. Now I'm screwed!
Here's the broken assembly detail
Frustrated I hit the internet and I discover (by luck) that the faucet is a Price Pfister Marielle. On the horn with the company and they next day deliver the replacement part plus some additional o-rings and a new diverter (just in case). Total cost was $12 for the next day delivery. All put together again and works like a champ - just in time for our Halloween night party!
Thanks again for all the advice.