Potential positive results.
 

I have an 84 Volvo 760 2.4t non egr. Junkyard pull. I rebuild the pump and replaced nozzles pop tested etc. timing ok however there was a blue black haze at idle and at temp. Here's what I did last chance before a rering and bearing change.
1. Removed injectors and filled cylinders with Berryman carb cleaner 0996. Filled each cyl 4-6oz each. Left overnight. Drained oil and replaced filter with full synthetic oil. Berryman came out of drain plug with the oil.sprayed a can of brake cleaner into the drain plug hole and let drain.
2. Sprayed brake cleaner liberally into each cylinder 2 cans .disconnected glow plugs and spun engine over blowing crap and material from the bores.
3.installed new heat shields and injectors. Bled and started. Went for hard road test 30 mins.

Result. Smoke has definitely reduced at idle. So maybe the long soak overnight freed up the oil control rings and or piston rings. Dipstick blow by is reduced and the crankcase oil was clean after the 30min run. I'll keep posting results.
Maybe it'll save having to tear down the engine

Nice. Do you think your hard road test 30 mins. helped much to improve the results? Did you do similar hard road test 30 mins. before doing the solvent soak/clean/purge? (Trying to establish a benchmark).

Presuming the problem was stuck rings/clogged ring lands, running full synthetic motor oil should help loosen things up further over time.

I am a big fan of doing the "Italian Tuneup" from time to time to keep these engines healthy.

Yes I did hard road tests before and was getting to the point where I’d have to do something. Judging how harsh the chemical attacks carbon the long soak overnight the chemical seeped into the oil pan. Once it started it pumped out black gray smoke and after a hard run I let it idle for 30mins. There is a noticeable decrease in smoke. That was my experience.

Good to hear. Sounds like your methods definitely helped.

The diesel fuel that was available for the first 20 years of these engines' lives was much poorer quality and higher in sulfur content than the fuel we have now, and engine oil quality used to also be much worse, plus the dealer recommended oil change interval was too long. That resulted in a lot of the motors spending much of their time running on dirty fuel and with thick, dirty oil that wasn't good for long term durability. Some of them wore out early as a result. But now with much cleaner low sulfur fuel and affordable high quality synthetic oils on the shelf of every parts store, if you can get the inside of the engine cleaned up, and it's survived to this point without too much internal wear, it's easy to keep it clean going forward. If you do, these engines are pretty much impossible to wear out. Just have to keep them from breaking a timing belt or getting hot and keep them full of good clean synthetic oil, and if you do, service lifespan is more or less indefinite. :)

You might want to do another oil change pretty soon after driving a little to make sure you got all the solvent chemicals out, those might be hard on things like bearings and rubber seals if the engine ran a long time with some amount of them in the oil, though most of it probably would evaporate out.