Low oil sending unit plug into oil reservoir is loose.

So, my girlfiend has a 2008 RMK 600. The rubber plug that goes into the oil reservoir that is part of the low oil level system doesnt fit tight any more. I noticed some oil on the side of the reservoir and traced it up to the rubber plug that the wires go through. I took it all apart and cleaned the rubber plug and the inside surface with alcohol to make sure that it would be a good fit when I reassembled it. But, the plug is not tight and could leak if the sled ever ended upside down. Any ideas on how to make that "connection" tight again.

Thanks in advance!!