While in Florida where my son lives we checked both of his Fords over. Eyeball maintaince. He has a 05 F150 and and a 06 Expedition with the 5.4 Mod V8. I took off both oil fill caps and had a peek inside. Both engines had a lot of varnish from what I could see. Each has about 60,000 miles and he has been running, in my opinion too far, 7-10,000 miles OCIs.Also the F150 was a tad gunky around the oil fill hole and cap. Since he has all maintaince done at the Ford dealer they use MC 5-20. Years ago he used M1 oils and did 10,000+ mile OCIs and always had very clean engines, so he just assumed the MC was good to go for the extended OCI. Bottom line he says he will have Pep Boys use M1EP in both engines.
Just as a side note I did 10,000 mile OCIs in my old GM 4.6 with 10,000 ile OCIs for 218,000 miles and never had any varnish at all. I'm sure the MC is fine oil but don't abuse the OCI.