Just hacking around in the garage, I noticed my oil drain recepticle had a fair amount of sludge in the bottom. It was the one for my 2 quart system from the lawn trackter. The accumulation occured over 2 years/6 oil drains. Just for kicks, I thought that perhaps a little fresh oil and some agitation would dissolve it. No chance, dino nor synthetic. LC had very little impact on it either, staight, nor a working dose. HGowever, ARX in oil rather quickly dismantled it. I was quite suprised, thinking ARX was such a slow cleaner. I am impressed.