I have a box of mushy, student-grade oils with a higher ratio of vehicle to pigment, left over from art school. They appear to be okay, despite time. By chance, has anyone experimented with using softer paint in the final layers, where you ordinarily would be thinning your (firm) paint to stick?
Mushy paints over firm paints?
Ian_Adkins No not really. I did buy a large tube of bob ross titanium white which turned out to be a lot runnier than it should be. No good for breaking on a mountain, so I used it later on in the paintings where thinner paint is best and managed to use it up that way. I guess what you are faced with is a similar thing, I'd try using it in your final layer, highlights etc.
You might want to check out this article that was written in the Blog portion of this site: https://blog.twoinchbrush.com/article/paint-better-mountains-upgrade-your-titanium-white/
I've used it once to dry out some cheaper paints I have, and I could definitely notice a difference, even as inexperienced as I am.
I did my first painting "all wrong" from home made liquid white, to having too much on the canvas, Blick oil paint while good are "runny" for this kind of painting and the classic very wrong brushes 
Somehow it all worked in the end but with alot more effort than it should have been. The few BR paints I've bought have been very oily when opened. I just got a new complete set as an experiment. The brushes matter more in my mind. You can compensate for runny paint.. you cannot add bristles or make them hold a shape when they wont do it. I have used both a very cheap plastic knife and a real BR knife. Both work equally well so long as you dont abuse the plastic one which will snap if you get too excited with your scraping