How to fix the drain when the ring under the drain itself has dry rotted causing leakage?

Hi Pdp

I'll need more info. To be able to help much, OK?

Tell me what kind of pipe is in place (copper, PVC, ABS, etc.). Approximately how old is the shower unit? How accessible is the drain assembly? What seals the pipe to the drain assembly right now... rubber seal, lead, or simply cemented on (lift drain grate to see)?

Let me know, OK?

Mark