An older mechanic once said to me.
"Oils don't fix synchronisers. Oils fix oil problems"
 
Basically if it has  a synchroniser issue (worn or damaged), oils will not rebuild them or repair them. A different oil will however fix an oil problem, where the is additional wear or impairment caused by the use of wrong or old oil.
 
TL;DR: If it needs a rebuild, you gotta rebuild it.

UPDATE:
Been driving for about 500kms+ now on ATF DEXRON III as recommended by Falcon.
Downshifting into 3rd is much better, it's SLIGHTLY notchy, but bearable in most cases indeed.
 
I'm having issues upshifting into 2nd though. When I rev past 4000rpm or so, and try get into second, it's very tough to get into. If I rev out all the way to 6/7000rpm and try powershift to 2nd, forget it, it WILL GRIND.
YES, I am depressing the clutch fully.
YES, I am keeping it depressed till I shift into 2nd, then letting go of said clutch.
 
I tried WAITING (although I shouldn't have to) for the revs to fall into the right spot for 2nd gear, but it STILL struggles to engage without minor grinds and notchiness, it will only engage till revs are 1.5k rpm ish where 2nd gear WOULD be at said speed. Of course that means when I let the clutch out by that point, then the engine will have to compensate for the low revs and bump it up to whatever will match the road speed on 2nd gear. *sigh*
 
It's just stupid.
 
I don't know what to do, might have to get a different gearbox. I'll finish up this tank of fuel and hit 1,000kms and see how I go.
 
Big thanks to Falcon!

You probably just need to replace the synchros, maybe only just 2nd and 3rd...

xez
You probably just need to replace the synchros, maybe only just 2nd and 3rd. Should be cheaper than replacing the whole gearbox...

I'd disagree on that... you can pick up good condition S54 boxes for under $400, even if you were to rebuild it yourself, you would spend well over that price. Just my 2cents worth.

100% agree Carmikey.
 
My mate has a good S54 box that I've tested myself in his car, absolutely fine. It's from a 91 MR2, so a bit older.
Anyhow, he said when he changes his gearbox to an E153, he can give me his for $500, drive in, drive out, labour inc. and all.
 
Which I think is a decent price considering he knows what's up.

So here's another update.
The S54 has been leaking, and it's very possible it's the seals for the output shafts.
I've totally sealed the bottom drain plug for the gearbox fluid, I thought it was the cause because it appeared to be weeping, but upon further inspection, I noticed the leak is likely to have been coming from up top (the output shaft), or both even. Anyhow.
 
I'm not 100% sure on the part #, and I'm not 100% sure on the process used.
 
Can anyone direct me to a guide that is fairly accurate for the MR2.
 
I was told to replace the output shaft seal (picture of leak/problem area attached), and from looking around, I've found 2 different things that I can buy, but I need to confirm the part #s first.
 
The 31115A looks like the correct seal, can anyone confirm?
 
Thanks for your help so far everyone.
 
Pictures: http://imgur.com/a/DpGTl
 

31115A is the axle shaft seal… and you need two if you're going to do both sides.
 
90311-30006 is the original Toyota part number (for the S54 transmission, not the E153 from the GT/Turbo).
They now have two updated numbers for the same seal which is 9031130017 and/or 9031130019.
 
You can order them from Amayama for under $5 each, or get an equivalent Febest seal off eBay:
http://www.ebay.com.au/it...3ee:g:skkAAOSwMmBVojUd
 

Awesome.
Thanks Mister2.
 
I made the right call and ordered the 31115A, but only one, as the right side was dry as a bone.
 
I already made the order through Toyota for $16, it's worth it considering I am picking it up tomorrow morning!
 
Thanks once again for confirming this.
I'll let you all know how it goes.