I just decosmolined a Yugo SKS. Using mineral spirits soak the small parts in a trough & the receiver/barrel in a length of PVC pipe. Scrub with a bristle brush; a fridge condenser brush works for the stock inletted areas. Rinse with hot water & set aside to dry, took a few days for mine.
What emerged was a like brand new SKS.
Take it out on a sunny day and run 100 rounds through it. You'll be amazed at what seeps out.