If you use the stuff from gm it has the additive in for the G80 diff and it smells like grapes it is a little pricey but it works good mine took right at 4 qt's to fill
Me,Wife two boys ages 20 and 18 also two dogs
2008 Dodge Ram Quad Cab 4x4 6.7 cummins
2008 Jayco Eagle 341 RLQS 37' with b&w turnover ball & companion hitch
using rotochoks
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If you are using synthetic oil in the rear diff you do not need the additive. Go to the dieselplace.com if you don't believe me. Here is a quote that summarizes many of the posts there.
"Do some searches, there are several threads that reference studies done by Eaton (manufac of G80) and IIRC, the top three performing gear lubes were Amsoil severe gear, Mobil 1 synthetic and then one by Texaco that is actually what GM buys in bulk. As long as it is a synthetic, GL-5 rated gear lube you should be fine w/o the additives. I use the Mobil 1 75W-90 syn w/o additive and it is fine."
Dave
From experience, some synthetics will not work. But I know for a fact that Mobil 1 will not work without the additive. It's cheap insurance to put the $5-10 bottle of GM additive in the first time rather than having to drain some oil out through the cover to add it in on the second try.
Mav
'08 Dodge 3500 SLT Mega Cab Dually, 6.7l/6 speed.
'08 Winners Circle 36SRV-H5
Pair of '09 Polaris Sportsman 550 XP's
'05 Polaris Trail Boss 330
'03 Yamaha TTR125LR
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