The warriors clutch isnt really all that modern though... i dont think they have changed the plates since the early 80's
Its still considered a modern design, a lot of stuff from the 80's still is
The material in those fiber plates has changed at least 3 times in that period that I know of (probably more). Manufacturers are always making changes and upgrading materials for consumables like that. Sometimes the part#'s change, sometimes they dont.. Yamaha, Suzuki, Honda, etc, they all do it.
Generally it was the old fiber plates that had a problem with certain synthetics and/or EC type oils, or misc oil additives. It wasnt very many either. The main problem was with certain oil components such as molybdenum and graphite, they would get 'absorbed' and/or cling to the old style fiber plates. It didnt take long for them to become useless and slip like crazy.
I've seen a few plates that ended up like that from using the 1st Castrol Syntec put out (this was quite a long time ago, the current stuff has changed since then). Even though it was marketed as a "Synthetic", it was still a Group III base-stock (i.e. dino oil), some of the additives they used to increase wear resistance would react poorly with certain fiber plates (a couple Hondas particularly). Slip-O-rama within 50 miles of use.
Most manufacturers have change their materials for their fiber plates, not to mention the old additives for oil are now restricted or just no longer used.
These days, when I see somebody get slippage from switching to a synthetic, its usually nothing more than an already worn clutch that the synth oil is exacerbating. This happens sometimes on Bandit 1200's, and a simple fix is adding 1 Barnett heavy-duty clutch spring, problem solved. Of course, some guys just put in new plates too, as they were probably due anyways.
Diesel oil doesnt shift as smoothly as I peronally would like, but it does work good for wet clutch applications. A lot of guys run Rotella Synthetic 5w40 in their Bandits on my own site without issue, as well as a lot of SV owners I know. Its cheap and it works good, hard to go wrong with that.
I've been running Mobil-1 10w30 in my bikes for a long time without issue. It also went in both my Raptors on their 1st oil change, they shift great now, and will benefit from Mobil excellent protection.