Went through the 95 / 96 / 97 codes and being unable to pedal dance program.... Long story short aftermarket key and IGN LOCK CYL !!
Key sense and Antennae circuits were hacked/disabled. Easy to check (now) by pulling Drivers Knee panel and Gauge lower WTH!!
Few repairs and was 20 mins...
First it is an external leak . . yay. Grab a can of Brake cleaner, engine degreaser and clean that spot well to see how bad it really is.
Grab some Subaru coolant "conditioner" they were notorious for headgasket leaks .. TSB TT0404-0002
Castrol GTX Diesel is applicable for gasoline and diesel light trucks
where SL or SL SJ engine oil are recommended. it has current certs.
As per Lexus
Oil grade: API grade SH, Energy-Conserving II multigrade engine oil or ILSAC multigrade engine oil.
No Problemo it's newer than your engine.