It really doesn't matter what brand or type of motor oil is used on the 400 as long as it is kept clean (I.e. changed regularly).
The 400 is a small high-revving (sometimes 6000 to 7500 rpm for hours) thumper with anti-friction (ball) bearings ton he crankshaft and rod big-end; it is much more important that the oil, whatever it is, be kept clean--by changing it regularly. This is quite unlike an automobile engine with plain bearings throughout; plain bearings can accommodate much "dirtier oil" than can the ball bearings in the 400, nor do most cars run 6k to 7.5k rpm for hours on end.
Consider that at 65 actual mph (6500 rpm) for 10 hours (650 miles traveled) the 400's engine has made 3,900,000 revolutions. An average automobile engine will have turned (assume 1800 rpm @ 65 mph) just 1,080,000 revolutions over that same 650 miles; fewer than 1/3 as many. This is also fewer than 1/3 as many strokes for the one piston in the 400, versus any one piston in the automobile engine.
As the laws of physics and properties of materials remain the same in either engine it should be obvious that our 'scoots are being subjected to 3 times the wear, producing 3 times the combustion by-products and depositing 3 times the amount of contaminants and metal particles in the oil than a car engine.
The early 400s like mine use 2.1 qts, the newer ones just 1.2 qs--almost 1/2 the amount of oil subjected to the same wear and tear and crud.
So, I change the oil in my 400, with 61.5k miles (48k are mine) on it, every 2000 miles--the filter every other changs--Suzi's 3500 miles recommendation be damned.
And despite my opening line I use Valvoline's 4-Stroke Motorcycle dino-juice (20W-50 here in Florida). Not because the 400 needs motorcycle oil (it has no wet clutch), however it's just $3.58 a quart at Walmart so what the heck.
I could have probably used their "Super-Tech" house brand over those same 48k miles and had no better or worse results--she runs like new...
Rotella is a good oil for bikes with wet clutches as it does not contain friction modifiers, which somewhat counter-intuitively increase an oil's friction properties and can make wet clutches "grabby".
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