The oil drips I have seen have been very clean oil so, at first blush, I suspect the transmission. But, then again, I first noticed it when I was inspecting for engine oil leaks the day after I changed my oil so it could be engine oil. There is a sheen of oil on the outside of the bell housing too, similar to the photo, so I guess it could be from the tube. I haven't noticed oil on anything else other than the bell housing but it's worth another look. I had planned on waiting until it was more obvious where it was coming from (after the engine oil gets dirtied up some), maybe I will still wait. I'll try to get a chance to crawl under before it's towed and look around some more.
I don't know exactly what to suspect on the engine losing power. It happened suddenly and didn't get any worse in the 5 or so minutes I drove it. I'm pretty sure it is a fueling problem. I would think that a fuel filter would clog up slowly and, if it was that, the problem would have come on more slowly. But, then again, I'm no diesel mechanic and I'm here on this site to learn.
Biggest problem now is I can't get a tow truck. They're all busy due to the snow. I can't do much here at the office. I think I'll do a test drive after it warms up today and see if it has fixed itself or, at a minimum, will let me limp home.