Castrol GTX 10W40 has been my first love.

I've been using Castrol GTX 10W40 in everything (old cars, tractors, dirt bikes, ATVs) up till the Savage clutch started giving up.  Going to 4-stroke motorcycle oil seemed to help a little, granted the clutch is on its way out anyway.  May just be coincidence, but now I'm questioning the GTX in the Savage as a possible clutch killer.  But I've used Castrol GTX 10W40 in my XR500and countless other wet clutch machines with no touble, and I never let up a bit.

Plain old Castrol GTX (red top) North American market 20W50. I tried 10W40. I tried blended, both weights. My bike works best with dino 20W50. It is cheap to buy, I can get it anywhere from the Arctic Circle to the Yucatan, it doesn't burn off/magically disappear like syn did.

When I (illegally by USN regs) rode in Spain, I used whatever was cheap. Granted, gas and oil weren't cheap in Spain in 95/96, but no bikes I borrowed had problems. Air cooled, liquid cooled, oil/air cooled, didn't matter.

Oil is oil. If your bike works fine on your normal brand, so much the better. I've even used the less than a buck a quart Wal-mart stuff without trouble. Don't make a habit of it, but, any oil in a pinch.
-WD

Very interesting fact-
couple of days ago I went to one of the local dealerships to get some oil / I buy it a discount price, so I pay  like for a regular car oil in Autozone/. I bought Suzuki 20W-50 and Kawasaki 20W-50. When I got home I compared the labels and I found out that Kawasaski brand was marked like a MOTORCYCLE oil , but on the Suzuki bottle was writhen just 4-cycle MOTOR oil , made in USA. I guess even the Suzuki  dealership was selling a regular car oil , but pocketing a hefty profit .
From all I have red so far I have come to couple of conclusions:
1. It is not the brand name- It is the interval between the oil changes that makes the biggest difference.
2. The oil loses the viscosity very fast- about 20% in the first 800 miles and after that the process slows down, but the oil stays thinner, so always I should put thicker oil, than what recommended.
3.If the clutch starts slipping because of the oil- It's time has come anyway. I change the clutch and put stronger springs or put more preload on the old springs to make for the more slippery oil. This is what "Barnett" is doing for their aplications.
4.Doesn't matter what kind of oil am I using, I always keep my eyes on the oil level.