Yup. Plenty. Both on the 'research' side and on the 'ongoing maintenance' side. This is quite common in tighter suburban, and urban areas.
Do you HAVE the Easement? Did you get it from the Atty, Title Co, or whomever-- or have you not quite yet started the legal DD?
Unfortunately, MANY of these were initially done on a handshake and then memorialized later. Others, you may find that the Developer tossed them into the site plan (esp during the 20's, 30s as cars became commonplace.) In these cases, maintenance was rarely contemplated, but newer drafts will usually do so, if a proper Atty or Title Co. was involved.
-- one thing to take out of your head-- for MOST easements, 'whether or not it was paid for' is entirely irrelevant to you today. It just doesn't matter any more. If you also need the 20%, then you don't have a driveway without them, same as they don't have one without you. Plus, your predecessors agreed... and that's that.
One exception to that last statement is an Easement in Gross-- because it runs to the party NOT with the land. If you find that it's an Easement in Gross, then you can maybe charge a new party for the continued use of the access way. Consult an atty.
No matter what, you need to get your hands on that doc. if you're ADAMANT that there be an ongoing maintenance agreement, you can make your purchase contingent upon the Seller acquiring it from the neighbor, but don't be surprised if you lose your purchase over a move like that.
Hope that helps.
Steve