If Mobil has indeed discontinued Omega, then their Sigma cutting oil will work in its place. I've used both with good results - the only reason I bought a pail of Omega in the first place was because Mobil's product guide showed it has roughly twice the amount of sulphur content as Sigma. Our local Mobil distributor had a hard time finding a pail of Omega a couple of years ago when I asked for it, but IIRC, they had Sigma in stock.
Mobil seems to have replaced Texaco as the major supplier of industrial oils in this part of the country over the past 30+yrs.
I tried Cool Tool II before switching to the Mobil oils, and got a lot of chatter when reaming chambers - don't know whether it was my technique (these were the first few chambers I'd cut), or ??? But I sure like the finish I get with the Mobil products.