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Castrol TWS 10w-60 is recommended by both zfdoc and ZF. Otherwise, zfdoc recommends any synchromesh fluid (Pennzoil, Amsoil, Valvoline, ACDelco, etc.).
"TWS" reportedly hasn't been produced for many years. Difficult to use something that isn't available. This quote is from one of the linked threads, from 2019. 5 years ago. Looks like Chump hasn't been able to source TWS since at least 2016. Probably no one else has been able to either.
I keep this oil on the shelf for one of my non-Corvettes. Note the viscosity. When I was researching this oil about a year ago looking for a less expensive way to obtain the same oil ($24.50 per Litre for an oil change that uses 9.5L gets my attention), it seems that it is made by Castrol, there are two formulations for Castrol 10W-60, and that one of them, "TWS" was no longer available. I found it from a Porsche dealer with an online presence for about $85 for a 5L jug. They also have the 1L cans, about $16 each. The metal container with the graphics it comes in probably increases the price too, but is pretty cool to look at on the shelf.
So, another possibility for a "10W-60" motor oil, if that's what you want to run in your transmission. I don't. I put 10W-60 in my air-cooled flat-6. Delco "Syncromesh" goes in my ZF-6.
This post has been quoted below. Quoting entire posts is lame, and makes threads difficult to read.
Fair enough. I was only able to find the "Edge" formula over the summer and I was too paranoid to use it so I went with Pennzoil. Didn't know it was effectively impossible to source, though. Good to know.
