Drive Axel - Gear Oil Weights / Conventional vs. Synthetic

[EEqualsMCISquared]

Hey there bus nuts,

I bought our lovely "Ruby," a 1998 MCI D last year, been getting her ready for a cross country move from Lost Angeles (pun intended) back to Georgia.  My mechanic has been doing things to get her ready; lubed everything, adjusted brakes, etc.

While checking the Rockwell Drive Axel, he found some metal shavings on the magnetic Drain nut and some slop / play in the axel.  He showed them to me - not a lot of shavings but a bit of slop.  Bus drives and sounds great, though and was babied by its last owner.  However, it was mostly sitting since Covid until I bought it so about 2 years of not much activity.

Should add the bus has 1.4 million on it BUT had an in-frame engine rebuild about 200k ago, so she's real clean and runs smooth.

Here's my Qs:
1) MCI says 80w/90.  Most places I've checked with (like ABC Bus) use 85/140 GL5.  I'm leaning towards 140 b/c I'll be full up with moving stuff and towing a Toyota - though probably not up to the 44k weight capacity of the bus.  Plus, I'm traveling the Southern route to GA AND I won't be taking her out again until Spring Summer, likely South to Florida.

2) I'm leaning Conventional over Synthetic - b/c that's what some have recc.

3) I'm leaning towards paying a little more for something like Lucas over Master Pro or Magik or whatever, because I know the name and... well, how often do you do this oil change, after all.

What says you guys?

Ruby is: A 1998 MCI 102D.
Detroit 60, 12.7 liter, Allison 500 Trans.
1.4 mil with in-frame rebuilt 200k. ago.

[luvrbus]

I would use the synthetics and forget about the Lucas 

[sledhead]

I would use the synthetics and forget about the Lucas

x2

as with syn you should never have to do it again

[dj]

as a retired trucker and have owned several trucks over the years as well as having a bus conversion i would HIGHLY recommend synthetic oils in the hubs and drive   kust sayin

[dj]

oops fat finger....was supposed to be just sayin....my bad

[tr206]

Maybe you should check your wheel bearings could be the cause of shavings on the plug not sure if the wheel bearing are still grease packed in 1998. I use schaeffers 140 wt gear lube for what it's worth.

https://stores.buy1oils.com/schaeffer-0209a80-040-moly-universal-gear-lube-w-red-dye-sae-80-to-140-or-iso-150-to-680-40-lbs/

https://stores.buy1oils.com/schaeffer-0294140-040-supreme-gear-lube-sae-140-or-iso-320-40-lbs/