If engine and/or transmission service is performed wherein the transmission has been disconnected from the engine, pay attention to the two required alignment pins on the rear of the engine block.
If there are less than two alignment pins present, one (or both) may have been removed with the transmission/transaxle assembly. Be sure that both alignment pins are installed on the engine block prior to transmission installation.
If only one (or no) pins are present, this can easily result in failure of the transmission/transaxle.
Lexus released this TSB, relative to all 1990-present models. Naturally, block-to-transmission alignment pins are required on all engine/transmission assemblies, regardless of make, model or year.
LEXUS ALIGNMENT PIN P/N: 90250-10113