Marijuana smoke migrating to my condo!
I would consider adding a positive pressure to your living space with the fresh air being pulled from a wall on the opposite side of the house. I have installed this type of fan in several multi-family dwellings to keep smoke stink out. The ones I have used are quite small squirrel-cage blowers that operate with a pressure switch; I think it was based on 2 or 3” water column. 

The slight positive pressure pushes air out through light fixtures, switches and outlets.  The only downside I remember: because these are small, if you open a window or door for long you lose the advantage of the positive pressure. I did a handful and put each one in a wall next to an existing outlet so no new circuits needed to be run. 

I don’t know if you can really seal things but the positive pressure fan worked. I had 1 customer have me install them in 3 different houses; the last one was a single-family home but she said she liked the fresh air (that house had no make up air electric baseboards) and it made her feel better, so those little positive-pressure fans do work.