Heh, I had a similar encounter at work a few months back.
'13 or so Altima with the 2.5L and 64k on the clock came in for an oil change; nothing special, though they wanted the cheapo 5W-20 oil change instead of something better with 0W-20 (which is what the car calls for, but I digress). Anyway, I pulled the oil cap off and was greeted by the site of sludge. Looked inside the engine, and aside from the sludge where the cap sat, it didn't look terrible. After talking with our lead tech and service manager, I went ahead with the oil change, though I made sure to document the sludge. Very little oil came out, though, like a quart and a half.
The filter, though...the paint was coming off of it, and it looked like an OE Nissan filter; I believe that's sludge on the baseplate (I don't have a filter cutter, sadly; this would've been interesting to take apart). I'll let you all do the math here.
I put one of our filters on, filled it with the cheap stuff (again, this is what the customer asked for), and crossed my fingers. It fired up without issue and idled like any other QR25 I've encountered. I programmed the oil change monitor for 3k, wrote the sticker out for same, made sure I documented everything I did on the electronic RO, and sent it on it's way. Haven't seen it since.