Here's an Interesting Problem

[oddball]

Also, is there a known date or VIN after which improved tensioners were used? That would be great to know.

It's been posted before. I forget the detail, but the transition was in the 2001 model year.
Taking off the passenger valve cover only takes a few minutes, then there's no confusion. Driver's only takes a little while longer, although a bit more creativity.
If you haven't already, start collecting unique tools. Lots of 1/4" drive ratchet extensions and swivels, deep metric sockets (esp 10mm). The floppy-end ratcheting wrenches have saved me many times on this car.

 

[PRSPlayer39]

Yeah, I haven't had any codes related to injectors. but I'm still thinking oddballs idea of the leaky injector makes the most sense. A slightly leaking injector might not throw a code.

Hoping to tackle the injectors this weekend. Good advice on the 1/4" drive and box end ratchets. Already started building the collection on the sway bar bushings job