Help! Section 8 tenants with no lease

[Andrew Robbins]

7 years ago I bought my first triplex and inherited existing tenants -- Los Angeles rent control, all Section 8 tenants. Didn't know anything back then -- got a copy of the estoppels but not the actual leases.  Now I want to sell the building, and for one of the units, no one can find the original lease (they've been living there for 15 years) -- not the tenant, not Section 8, not LA Housing, no one!  Seems like the commons sense thing to do would be to have the tenants sign a new lease, but I'm told I'm not allowed to do that either because of rent control or Section 8.  Advice?