Koehring 6620 lost nearly all hydraulic power

My Koehring 6620 LC5 excavator has very limited hydraulic function - nearly all of a sudden. The fluid level was confirmed full less an one operating hour ago. When I was brought in on this issue, the level was just below the low line. I see leaks (don't you always on older equipment), but nothing that rises to the level of losing 5 gallons of oil. The right track has some power. The left track has no power. I cannot raise the boom except at high rpm and even then it barely goes. The house turns fine. I topped off the hydraulic fluid level and saw no change. The primary leak that I see is where all of the boom hoses connect - into some sort of cylindrical manifold. The leak is in a machined inner housing that may look like it popped up more than it should have. Now for the missing piece of information...I have a new guy doing some work for me. He's a really, really awesome kid (26) who is very mechanically inclined and wants desperately to do the right thing always and isn't scared of getting dirty. He moved the machine the other morning to install a replacement muffler and called me after he had moved it maybe 250 feet to say that it had no power. My fear is that whatever seal has blown out did so as a result of the fluids not being given the requisite 10-15 minutes of warm-up time on a 35 degree morning - I've confirmed now that he didn't just start and go, but there were only a few lights reading on the temp gauge when he did go. Maybe someone can tell me 'no way that THAT would ever happen'. It'll kill him if he learns that he might have caused the issue, but at the same time I need to relay the importance of proper warm up procedures. Thoughts on what failed? Thoughts on whether a lack of warm up could have caused it?