The original part number for the A/C drain tube is 3503133. That part was superseded to 3848827 – which I found one on eBay https://www.ebay.com/itm/85-86-DODGE-PLYMOUTH-CHRYSLER-NOS-MOPAR-A-C-UNIT-DRAIN-TUBE-3848827/222519643479?hash=item33cf344d57:g:URIAAOSwIaFZIiAQ 3848827 was superseded to 56004538, which was superseded to 55036054 – which can still be purchased new from Chrysler for $5.45 (US) (as of July 2018). Basically, this part is the same, correction: basically, this part will fit all Chrysler body designs from early ‘60’s to 2000 or so – but the shape, the exit or the retaining clip has changed over the years. I hadn’t measured it – but think the hole is about 1 inch in diameter (don’t quote me on that). The exit is pinched off, so water will drain out but bugs and such won’t craw inside. Mice like to go through there and make nests (which I think you have experienced. Which version tube you use will not matter much. Anything is better than nuttin’. I replaced the heater core on my ’86 Fifth Ave a decade ago or so. The wire retaining clip (molded into the rubber) on my original had rusted and crumbled when I removed it – so I bought a new one (then). The old one could have been reused with a zip tie, if I had wanted. Personally, I would just go to a pull-a-part and walk around and grab one from a newer Mopar. It requires no tools – and I seriously doubt they will charge you for the part. That said, I highly recommend having one in place – or this can happen. Well, to be honest, the same can also happen from debris getting into the cowl area – but not to the same degree as it is getting carried inside by various multi-legged critters. On an unrelated note: If you have an automotive A/C that is not quite working as well as it should, and you can either feel a cold wet passenger carpet area and/or you can hear water sloshing around on turns (this applies to any vehicle). The first thing to do is stick an object (screwdriver, ink pen, stick, etc.) into the slit on the A/C drain tube. In most cases, a flood of (cold) water will come out and your problem is solved. Every once in a blue moon (not often), something stops up the slit and a little intervention is needed it get it going, again. BudW Edit: a file photo of one.