Hey, just one more idea... I am figuring that this issue is a result of the new sink drain not lining up with the old drain.
One quick fix that works perfectly is a corrugated, flexible 1.25" x 6" tailpiece...see pic. (you may need to purchase an 1.5" x 1.25" nut and washer if have 1.5" ptrap...
Here, you would cut the metal or plastic tailpiece coming from sink pop-up assembly and you would cut it so that you could slide the COMPRESSED tailpiece into place. When tailpiece extends will seal joint nicely AND ALLOW FLEXIBILITY TO PUSH THAT VANITY TOP BACK TO THE WALL (add a little bit of caulking and wedge the sink in tight overnight).
That should be all you need to do...If I understood this question right..???
Let me know.