1983 wr 250 gearbox oil?

I was wondering if there are better oils now for my 83 gearbox instead of the SAE 20 per the manual?

Yes, there is. Without wishing to open yet another oil debate ....
I have been using Silkolene Medium Gear Oil for the last 35 years, and I've never had a gearbox or clutch issue.
Everyone has their favorite.

I like a hybrid mix of 300ml. Coconut oil, 900ml. 90 wt. Royal Purple, & 400ml. KY lubricant =1600ml. But I hear a lot of guys swear by ATF type F

SPECTRO golden gear. 80w

Thanks. I have heard also that atf is used in the gearboxes.....I recall ATF in forks but is ATF a bit light for gearbox?

In my experience, using ATF in straight cut motorcycle trans results in quite a bit of visible metal in the oil... Several years ago I contacted Maxima Oil... they sell ATF and wet clutch gear oils and they told me due to the popularity of racers using ATF they tested both side-by-side in their Supercross team bikes and measured significantly more trans wear with ATF. Their ATF was the more expensive product but they recommended not using it and using their MTL line of gear oils. They said that straight cut motorcycle trans gear teeth are narrow and highly loaded compared to planetary and helical automotive trans gears and the motorcycle trans has different lubrication requirements ATF can't meet.

That said, many swear by ATF and I think KTM specifies it in some of their new bikes.

Then I found the original letter I received from Malcolm Smith Motorcycles with my new Husky several decades ago and they recommended Torco gear oil... I've been using Torco MTF-L since and have been very happy with it.

Note that the SAE uses two completely different rating scales for motor and gear oils... a 75w gear oil is equivalent to a light weight motor oil.... Maxima says their 75w is approximately 10w-30... I think Torco told me their MTF-L is equivalent to 20 weight motor oil but I don't remember for sure... it's what they recommended. The Torco stopped the cold "clutch drag" completely.

Viscosity Grading System Chart for reference:

ive been using briggs and stratton oil in the 400 lc, no probs, great clutch action...have used Atf F as well with good results...the trick with ATF is to change it regularily

Atf but change it often