Well, since yesterday I had my car up on the lift to drain and refill the rear diff for a 4th time. First I'm a little annoyed at the difference in price between dealers for this GM LS diff fluid. Called my usual contact and they only had 2 bottles for like $38 each. Last year I bought 3 bottles for only like $22 each (still have the receipt from Spring 2021). Called another dealer they had none but charge $55 each.

Looked up Tubman online and they were good only $19.xx a bottle but shipping to me in Toronto from Ottawa is like $14 bucks for 3 bottles. Finally I checked Old Mill (Jane/St. Clair) they had lots and was about $25 each so I decided to pick up 3 of them there instead (basically similiar pricing to Tubman with shipping and no waiting).

There's two other brands that I've found that is LS 75w90 gear oil made by Mobil 1 and PetroCanada. I'm wondering if either of these 2 fluids will be the same fluid as the OE GM stuff (my feeling is perhaps the GM LS oil is repackaged M1 LS gear oil but I don't know).

So yesterday aftn. started draining out the gear oil after driving the car a bit, fluid came out fairly warm but not hot and looked slightly darker than the new gold colour fluid so my previous 3 drains is helping to "clean out" whatever gunk might still be in there. As I didn't want my garage to stink of gear oil after I drained out to a steady drip I replaced the plug and poured the old fluid into a container then left the pan under the diff again, removed the plug and left it to drip till today. I collected just under 3 litres of gear oil into the container so when I pump in the new fluid it should be close to 3 or a little over before it starts dripping out of the fill hole.

I might "slightly" lift up the front of the car to put a rear angle at the back to see if more comes out but have to check to see if my jack goes up high enough with my car at the lowest lift point later this morning so we'll see. This one for me should be the last time I'll change gear oil for a few years before needing to do it again. I had only put about 2000kms on the car since this spring after changing a 3rd time and the ZR1 will be going into storage soon after this is done.
 
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Finished it up this aftn. Ended up taking just over 2.8L of fluid that I pumped in before it started dripping out the fill hole. I pumped a tad more so it was a slow steady drip before stopping and getting the fill plug up there and tighten up. A real PITA getting the fill plug up there while trying not to drip too much and wasting the excess fluid.

A more of a PITA is the new bottles they put the gear oil in now as seen in the pic. My manual pump screws into the previous bottle shown on the left. Lucky I still have 1 of those bottles that had a couple hundred ml of fluid in from the last change so I had to add fluid from the new bottles to the old one before going under the car and pumping (that means after 1L went in had to climb back up refill and back under 3 times).

When I get the car up again for winter storage I'll pull the fill plug and see if I can pump a few more mls in and put the plug back without too much dripping out. I'm finally thinking the diff probably takes more like 3 quarts instead of litres cause 2.8L=2.96qts so close enough to 3qts.


Mobil 1 LS gear oil 75W90:


PetroCanada LS gear oil 75W90:

 

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So local GM dealers in their infinite wisdom decided that the cost for GM LS gear oil should be stupid priced and now it seems also the M7 fluid. As posted above I was able to get 3L of dexron gear oil from Old Mill last year for $25 each this week I called them and it's now $37. M7 fluid (88861801) is now around $16-17 dollars/L.

This time Tubman earned my business. I just did an order with them for 4L of M7 fluid and 4L of LS gear oil. I really didn't need 4L of the gear oil but got it anyways so I didn't have to pay shipping (orders over $100 ship free so I might as well get something (extra litre of oil) than just paying same amount to ship the order).

$18.15 for the gear oil, $7.65 for the M7 fluid. Once my powertrain warranty runs out I most likely will switch to either Amsoil or Redline fluids for the drivetrain ALA I can confirm they are suitable replacements for the OE fluids used in the trans and diff.
 
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