Another vote for Auto-RX. Also, another vote for scrubbing off whatever you can with a brush and kerosene. Auto-RX doesn't typically release big chunks of sludge/deposits. It's not a flush. It's a slow-acting additive that is ester-based. When you add it, it basically has an affinity for metal surfaces and will emulsify deposits as it tries to attach itself.
If you go with seafoam or any other flush type treatment, you need to drop your pan and inspect the pickup screen.
Also, folks, be aware that the "detergents" in oil are not like scrubbing bubbles or Dawn. That's not their job. They are tasked with holding deposits in suspension as they form, not cleaning existing deposits off engine surfaces.
As for the efficacy of Synlube in preventing stuff like this, I'll leave that for another thread. Waay to much to go into here.
I cant tell your vehicle from your avatar icon but if that car has the HLA lifters like mazda engines I would be careful with hard solvents. there are tiny tiny HLA passages you need to worry about. if your valve cover is off its not hard to service them and put brand new ones in anyway 100 dollars US for the pieces and new upper gasket kit.
For comparison, 160k miles using various synthetic oils changed every 7000-10000 miles.
not bad, looks almost the same (keep in mind my engine is 28 years old and has had oil from 1980-2008) lol
heres gonna be a interesting discussion topic:
these are pictures of the inside of my model A engine thats been sitting outside for the last 50-60 years(not running)
and heres what the outside looks like(looked, got it fixed up and running now)
and where it sat for the last 50-60 years
when i dropped the pan it had about (guessing) 3 qts/5 left in the pan with about a 1/2-1" layer of sludge, mind you its last oil change was prolly in the early 50's (was used from 1929 - 1951 according to the last plates that were on it) thats non detergint oil that had oil change intervals of 500-1000 miles (no oil filter)
ill make a big long topic about the truck in general discussions...