Rain water was getting into passenger compartment. Local shop cleared the cowl drains but problem persisted. Top was in pretty bad shape and it was decided that water was entering the passenger compartment via the rear window seal. Top was replaced and problem appeared to be corrected. No water was noticed after moderate rains. However, after heavy rains water is still showing up in the rear seat area. The convertible top installer demonstrated that all front and rear drains are working correctly. My question is; "Could the drains be partially stopped up so that moderate rains could easily be drained but heavy rainfall would back up and overflow into the passenger compartment?" If so, what measures can be taken to correct this and are schematics available that show where all drains are located? Any help is appreciated.