Sean, The Registry of Deeds microfilms are now online at Familysearch.org. It takes a bit of effort but well worth wrapping your head around the system. You might want to read up on it before diving in, but it was more than likely registered. I usually first look in the Land Index books around the time I think the Lease was first issued, then look for the corresponding volume and Memorial number. How do you know they had a Lease for life? There might be some clues in the information you already have.