Before you remove the pump you might try removing the top plug (requires an allen wrench, and will be very tight) on the block where the lines attach to the main unit. If oil is pushed out that hole with it running the gear is probably there. If oil just trickles out, it may be that the gear has come off, as Bob mentioned. sometimes if they have set for a while they get air locked, and removing that plug and letting the air out while it is running may clear it.
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