avid elixir 5 - seals?

pylwagl

My 2013 Stumpjumper Evo comp has Avid Elixir 5 brakes (standard fitment), and I have always been pleased with them. however, getting back on the bike following a two week lay off I immediately noticed that when I pulled the rear brake lever it came straight back to the bars and didn't work the calliper. Previous to this, it had worked fine. Front brake is still ok. No leaks anywhere. bled rear brake and problem persists, although brisk pumping does improve things a bit (though only for seconds). Is it likely that the seals have failed in the lever end of the system? If so, how easy are they to obtain/replace? If not this, then what?
TIA
Stu