To answer your question: Found at Lowe's in the ODPE area. Absolutely fine as a quart add in - it may even "boost the performance of your other 5 quarts of Syntec (by OSP)
I guess guys here don't understand the reason for the high saps SL rating - though they all fawn over Mobil 1 0w40 FS.
I would like to see a VOA, sadly a lot of ODPE oils on the big box shelves are now mid saps - like the John Deere stuff.
Alternatively, the best professional advice would be to buy another jug of the - not castrol thankfully - Syntec (Omni Specialty Packaging) and take your extra quart to make six - from that "makeup" jug. - Ken
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About pro-select 10w30:
"We blend with high quality base oils and additives. We receive base oils and raw materials from Exxon, Motiva, Ergon, and Calumet. These materials unloaded via dedicated lines from rail cars or bulk trucks then stored in one of the sixty-two blending and storage tanks. With the additional load cells, we are able to blend by weight as well."
Prevents sludge and varnish
Multi-viscosity offers protection though cold-weather and high heat
Latest additives and superior base oils offer maximum protection
Helps engine run cooler
Meets or exceeds performance requirements for API CG-4, CF-4, CD and API SL, SJ, SH, SG