if you want mate i will do it on mine and take some pics and put them on here so you carnt go wrong, its easy job mate, takes 5mins. even if it aint come on again it will still be stored until you clear it, so you can find out what it was. ;)
my local toyota is usless, when i 1st got my gt i took it there for a full service, went to pick it up and they said they couldnt change the oil as they carnt see a filter! 1 of them chirped up and said"i dont think they have oil filters"! i got them to pull it back on the ramp and i had to show them where it was!
even tho the coolant temp senser is new it could be a dodgy one, it happens more than you think! anyone in your area own a glanza? try there sensor see if it sorts it.
yea you need proper gaskets mate, you wouldnt want to go thru the hassle of fiting it all, putting it all back together, starting it up to find its blowing like a hooker on a saturday night! because then youve gota do it all again!