Seal probably failed on it, if he was using 100% methanol, Like I said there reverse flow
check valve on that pump is not compatible with 100% methanol and it cold leak past and wreak some havic on the internals. He cold have also done something stupid with it like run xylene or toulene through the pump which basically destroys them. You never know what your getting with a used system.
I would be asking for a refund for the pump if I were you.