Did you use Castrol synthetic most of its life? If you did and are still having deposits then a couple of things to check. It's possible your driving habits were too much for that oil. The duration before changing might have gone longer than expected. Was it driven highway or in town mostly. Type of oil filter? Did you use high detergent fuel and or a pea additive to keep things clean? If you are interested in a quart of EC30 I may be able to help but I think you aren't gonna get the results you want. If consuming is high, on the cheap you need to perform my listed recommendation that I posted just recently.
Post in thread 'Does risoline high mileage oil treatment actually cleans the engine?'
https://bobistheoilguy.com/forums/t...ctually-cleans-the-engine.372152/post-6584448
if you're still caught up on trying to use a one quart solution after all that I have posted, get on Amazon and buy one quart of 5W30 redline oil.
Sounds like Castrol maintenance plan you have been running is not working well. Try a higher quality oil with a more strict regime and see if improvements are made. Good luck