Vacuum testing from the dipstick

[S50Sinner]

I have a 1998 2.5 5MT with a dipstick and what I suspect is a vacuum leak (codes 1124 and 1126, running fine at all temperatures), and I figured I'd shove a manometer into the dipstick tube.

Unfortunately, doing that gave me zero vacuum reading on the manometer.

Is there some sort of valve that prevents vacuum from reaching up the dipstick, or some sort of disconnect I'm just not thinking of? I would think that crankcase vacuum would be readable from the dipstick, seen as it reaches directly into the crankcase.

If my hunch is correct, that means I have a vacuum leak at the dipstick tube, which would explain why it's isolated from the rest of the system. Does this track?

More info:

Throttle response is good, no smoke at startup, oil level is 3/4 of the way to the top mark on the dash (exactly where I filled it to), I can remove the oil cap while idling with little effort, the car barely reacts when I do. I'd rather pay for a smoke test at a shop and find none than pay for a pair of O2 sensors and fix nothing, though of course I'd rather diagnose it myself for free if possible.