I don’t believe a bad guide would necessarily cause a poor leak down. The oil is coming from somewhere obviously and if you’re cylinder sealing up the chances that it’s getting by your rings, it’s not as high as it being sucked down the guide.
Obviously, you’re gonna pull the head off anyway to see that cylinder. And of course you’re gonna pull those pistons out before I broke down that short block I’d be looking at that cylinder head. The other thing it could be a guide bore if those heads have been reworked before. Take a mirror and face it up towards the guide in that exhaust port and see if it’s wet on the bottom of the guide where the stem comes out.