delay in Registration of sale deed

A sale deed if not registered, is not valid and the buyer cannot be said to be the owner. So, in order to get the deed registered, the original seller has to be found, and that original seller needs to register the deed in the name of the buyer (that is, the person who has possession of the flat at present). It can be done, but for that, the original seller, i.e., the person from whom the flat was originally purchased needs to co-operate.