LubeFiner: Thanks for that information. This morning I looked down into the engine from the oil filler cap and I can't tell definitively, but the cam shaft(s) appear to be slightly cleaner than when I was using Mobil 1. There's still a rich/golden-brownish hue, but by no means could it be considered sludge.
What I meant by stating that my mechanic was just seeing the beginning signs of sludge present itself is illustrated in this photo:
What my mechanic was referring to is the dark brown "film" on the top of the canister filter. He said that this indicated that I needed to do an oil change sooner.
RayCJ: Thanks for the link. I will definitely have my mechanic check that O ring the next time I take my vehicle in for service.
Virtus_Probi: It's has become clear that the information I obtained when I was researching RP was not entirely correct. Like I stated, my first clue should have been RPs refusal to disclose the type of base stock they were using.
RDYWAR: Thanks for the recommendation on the Driven FR50, but I'm not sure 5W50 would be the best choice for my engine. I've had several Mercedes Mechanics highly recommend either 15W50 or 20W50 for my engine. When I made the switch I came very close to switching to Red Line 15W50. The only reason I didn't was b/c RP was easier and cheaper for me to source. Red Line 15W50 is still a top contender, however.
RTexasF: Perhaps M1 is "synthetic," but I'm learning a great deal in this post. After researching M1 and their formulation change, I viewed their switch to group III base stock as more of a semi-synthetic rather than a fully synthetic. After reading ad_infinitum and tig1's posts, I now know that my reasoning was faulty. What contributed to my previous thinking was that Mobil sued Castrol over this very issue and the fact that European oils cannot market themselves a fully synthetic with such a formulation due to the more stringent laws and marketing requirements. At the time I did not fully understand that all oils were actually blends, but how these blends compare to fully synthetic European oils, I do not know. I guess the question boils down to: How is M1 marketed in Europe - as fully synthetic? Also, from ad_infinitum and tig1's posts, I now know that Mobil is now using Group IV in the form of Alkalated Naphthalene, and that some blends are using POEs (synthetic esters). Mobil 1 is also using more GTLs (gas to liquid) in place of any group 3 base stocks. So, it appears that Mobil is moving closer to a "fully" synthetic formula. Is my logic faulty here?
ZZman: Duly noted. I don't particularly want to pay a premium for a "fully synthetic" oil. Currently, the best price I can find on Red Line 15W50 is $9.72/qt., but I won't always be able to get that price - most of the time, Red Line sells for $13.00 - $22.00/qt., which is too much, not to mention it's not as easy to source as M1 or RP.
SubieRubyRoo: I'm beginning to think the same thing about RP. Certainly, it seems that RP is no better than M1 and may, in fact, be inferior. I think you may be correct that switching back to M1 is the answer.
Sloinker: This was my thinking as well and I'm interested in the answer. (some oils use base stocks that utilize group IV & V). Regarding Ravenol, it's too bad that it's a semi-synthetic here in America.
Does anyone know if the "motorcycle oil" designation of Motul and Liqui-Moly matters for use in a passenger vehicle?