I do know that a couple folks have succeeded in effecting some sort of repair of those involving carefuly (and lucky) separation of the plastic reservoir from the base, and possibly using some sort of sealant. But, my understanding of those round jobs is like Bob's, they aren't really meant to be serviced, just replaced, if leaking where you describe.
Although it means changing out other bits, including the lever perch, the rectangular type are rebuildable/serviceable, and I think, cheaper to replace than buying another round one?