I very much doubt there's anything wrong with your thru-hull. If there was a blockage there, it would be evident pretty much right away. I really think the issue is a combination of an issue with the condenser and the cold water - along with possibly the front unit being a longer distance away - and possibly a tired pump not pumping a sufficient supply of water. I know... lot's of variables there. You might be due for a line clean-out, though, which could certainly exacerbate this situation.
If you want to try an experiment, turn off the rear unit and plug the line (securely) so water only flows to the front unit.
"As for the statement that moving water does not freeze, rivers freeze, in case you southerners didn't know. I can send you pictures if you don't believe me."
Rivers freeze here in PA, too. But... flow matters - slower flowing rivers freeze sooner faster flowing ones and, besides, this is really a totally different scenario than a controlled temperature of flowing water through a pipe. In other words, in the case of a house (where this trick TOTALLY works), you have a constant supply of 60* water. With a river, the entire body of water starts to cool down.