Waterproofing rubber sleeve tore when replacing brush head.

I believe there is a sealing gasket that anchors the metal rod which connects the base to the replaceable brush. When removing the brush the upper rubber sleeve part of the gasket tore and the metal rod stayed in the brush rather than the base. Unit is unusable because brush will no longer stay anchored in the base. Can gasket/sleeve be replaced? If so, how? Thank you!