I'm going to start calling this forum 'the crackpipe' because I'm totally addicted. I find myself on here constantly.
Meza: I'm not much of an expert, so I don't know about the 2.6L engine. I've only heard about it on the M119 (4.2L V8). Interestingly, JimF and I have been emailing back and forth and he does not think that my power loss was related to the oil pressure at all. What I'm hearing from Jim is that he thinks the power loss was due to the dried out, collapsed tappets failing to open the valves fully. Maybe you have a valve or a lifter problem. Out of curiosity, does your engine have variable valve timing?
Placo: I'm pretty sure my E420 has the old-school M119, but I'm double sure my tech told me there are only two tubes per cylinder. I guess one tube feeds two valves. Maybe the 119 you're talking about is a different version of the same block.
As for the price per tube, I could be wrong, he read everything to me very quickly over the phone. I'll double check and update on Saturday when I get the actual paperwork. He did say that the new tubes are aluminum and are much higher quality. Maybe the price you are talking about is for ones like the original plastic tubes.
Someone please check me in to Betty Ford, I'm addicted to this forum.