Can you plug a puncture in an 18 inch pirelli p6 four season tire? It is not a run flat tire. The dealer told me they had to be replaced and they couldn't be patched.

Depends where the puncture is located. If it is located on the sidewall it might not be repairable. Something to do with weakening the sidewall strength. Might try and call a tire repair place and ask them. Dealer might just be trying to sell you a tire or there may be a legitimate reason it cannot be repaired.