I suspect this may be a hot topic that I've failed to find in other threads but I couldn't find any information elsewhere.
 
My E153 Gearbox has difficulty selecting 2nd gear. The problem is only on 2nd gear and basically I have to wait 1 second with the gearbox in neutral before selecting 2nd. Anything less than a 1 second wait and the box will crunch till the second has elapsed then go into gear. Going from a higher gear to 2nd is much easier and can go in if I match the revs via heel and toe downshift.

I have heard that Toyota made stronger Synchros for these gearbox's but haven't found any definite part numbers. I was wondering if anyone on here may spare some information as to the part numbers for the stronger synchros and any other parts I should also consider while the gearbox is out. A suggestion for oil would also be great. I've read so far on these forums that the GL4 oil is the way to go. Note I want to avoid Redline Shockproof like the plague, too many people have said its a bandaid oil that makes a car feel nice but also takes away from its longevity.

Any information is greatly appreciated.

How about where to find the gear box number? 

Many write ups out there on helping gearbox issues.  
Helping the feel / selecting - write up below and many more on the net;
http://www.mr2australia.com/bettergearshiftfeelforsw20in3parts.pdf
As per part two, the bearings was the best replacement, cheap and fixed my dead bushings.
 
Gearbox oil type and correct amount helps.  MR2 guys have also sworn by Royal Purple product.
 
I feel a better selection when after done the above write up and installed a short shifter (others all have there opinions but it helped me). However it wont fix worn syncros (very common in MR2 age).
 
Because of the age you may need new syncros / gearbox rebuild. Order parts from amayama (syncros bearings) then have a gearbox shop rebuild (about $2000-$5000 depending on how and what you do).

The only gearbox serial number is located on the edge of the square hole where the clutch lever passes into the bellhousing.

I appreciate the info. It's been a while and I've found a couple of things. Number one I definately have an open diff box, despite it leaving twin marks on the grass that I did the slip test on but all other indications prove open diff e.g. jack the car up and spin the wheel look for the other one and just general feel on the road would all lead to the conclusion that the car is open diff, not necessarily a bad thing still handles like its on rails but I'll upgrade later. 

Secondly after I replaced the clutch master and slave and bled it properly the clutch now feels a lot stiffer and also seems to have fixed the problem of having to wait a year in going from 1st to 2nd. There is still a crunch if you really snap second but it'll go in and you could do a smoking start if I wasn't kind to the box. But you can still tell that the synchro is worn.  

I've spoken to people about the redline oil and they all say that while its a band-aid oil it'll solve the synchro problem. I might price it up against royal purple which I know is nectar of the gods. I'm just weighing up keeping the box and fixing it or finding an LSD one somewhere, a few have come up for $1600 or so which isn't that expensive really. 

I will be looking to change the gearstick and bushings shortly. Thanks to the generous MrKrazyee I have a gear stick that hasn't had a hacksaw attack it. 

The right oil will usually make a huge difference to shift performance. Well worth a go.

Cheers

Speaking of correct oil, which weight should I get? 75w-90?

Matts_SW20
Speaking of correct oil, which weight should I get? 75w-90?

Yep, GL4 75w-90

I am having pretty much the same problem again.  A couple of years ago someone had suggested GL4? which was put in & made a difference.
 
Nik has suggested "Smurf Blood".  Which google says is RED LINE LightWeight ShockProof™ Gear Oil 75w-90
My car was in for service last week, & I mentioned that the gears were notchy again,but I forgot to ask them to use the Smurf blood.  They put new oil in, but it hasn't made much difference.  She needs to go back this week to have dizzy o-ring replaced.  Would it be an quick easy job for them to change the oil at the same time?

Yeah, I've always used REDLINE MT-90 in all my mr2's, I think its great stuff. Never used the light weight shockproof range, nor am I sure if its GL4, I thought it was GL5, but not sure.