Yes, visible vapor when you remove the oil cap could be an indication of excess blowby. One thing you should check is the function and configuration of your PCV system. If the cam box is clean I wouldn't expect sticky rings, but you could try a high detergent oil supplement designed to free sticky rings or lifters. Also, API CI-4 HD diesel engine oil has a higher dose of detergent additives and may free sticky rings. These are low cost things to try before you make the commitment to pull the head or sell it.
A leakdown tester should not be that expensive assuming you already have a compressor, and you might be able to rent one at an auto parts store or tool rental place.
My original plan on the CV was to just replace the valve seals, but when I got the cam carrier off and was able to wiggle the valve stems, I knew the head had to come off. The worst valve guide had about .030" clearance based on stem and guide measurements. The best was about .010". The valve stems were only very slightly worn, but the guides were WAAAAY worn. It only has 70K miles, but lots of high rev time since about 4000 miles of the total is race track hot lapping, and for some unknown reason the guides on these engines have a reputation for rapid wear even though the layout of the direct acting DOHC valve train doesn't place any side load on the guides. - certainly less than the rocker arms used on the 102 and 103 engines. Some things in life are just a mystery.