[TR] GL4 vs GL5 Gear oils

[Randall]

> Funny.  I've seen GL-5 spec oils with warnings on them....not to be used
> with yellow metals.

Quite correct, there are certainly _some_ GL5 oils that should not be used
with "yellow metals" (aka copper alloys like brass and bronze).

The point is, that is not true of ALL GL5 oils.  Some GL5 oils are perfectly
safe (and as noted provide more protection than GL4).

And, there are many GL4 oils that use the same additive that can (over time)
damage yellow metal.  They just usually don't contain as much of it (and so
produce less damage over time).  And some don't contain it at all.

IOW, the GL4/5 rating just doesn't specify whether that particular oil uses
that additive, or not, or how much it has if it does use it.

-- Randall