It may not have WS approval from Toyota, but…
“Use AMSOIL Signature Series Fuel-Efficient Synthetic ATF in transmissions and other applications that require any of the following specifications:
Aisin-Warner AW-1; BMW 83 22 0 142 516, 83 22 2 152 426; Chrysler MOPAR* 68157995AA, SP-IV, 68218925AB; DSIH 6p805; Ford MERCON* LV, SP, ULV; GM DEXRON* HP, DEXRON* VI, ULV; Honda/Acura DW-1*, Type 3.0; Hyundai/Kia SP-IV, SPH-IV, SP-IV- RR, NWS-9638, SP4-M; JASO 1A-LV; JWS 3324; Mazda ATF FZ; Mercedes Benz 236.12, 236.14, 236.15, 236.41; Mitsubishi SP-IV, ATF J3, ATF-PA, ATF-MA1; Nissan Matic-S, Matic- W; Saab 93 165 147; Shell M-1375.4, M-1375.5, M-1375.6, M-L 12108; Toyota WS; Volvo 31256774; VW/Audi G 055 005, G 055 162, G 060 162; ZF S671 090 255.”
…which is good enough for me.
The Aisin AW-55 in my Volvos is known for being weak and failure prone in the 2001-2002 models (yeah, I know, I’ve got three).
And yet, using various fluids that are “recommended for use in” transmissions requiring T-IV, or JWS-3309, vs. actual Toyota approval, hasn’t really led to problems. All three cars have their original transmission. One of the cars has 268,000 miles on the original transmission. All three shift great.