The fluid is pricy stuff and a little obnoxious to obtain too.
Castrol Syntorque LT is no longer being made. Not to be confused with Syntech...
You can still get the Mopar 4874459 or GM 12346190 NV4500 fluid for around $20-$25 a quart. Rumor was it's simply re-labeled Castrol Syntorque LT so it may not be available long term. Amsoil sells an oil that claims proper compatibility with the above GM and Mopar oil numbers.
http://www.amsoil.com/shop/by-produc...r-lube-75w-90/
If you can still get em... you used to be able to swap the stock carbon composite synchros out for bronze to be able to run a more available oil.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8
RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.