[Lewis and Clark]

Do any of you guys have the part number for an alternator belt for a 1996 series 60. It is a banded double belt. I have tired two single belts (gates 17500) and they worked for about 2k miles and need continuous tightening.
I have an old banded belt that was on the coach when I purchased it but it does not have any markings to identify it.

Thanks in advance for any help.
Nando