How many speeds does your tractor have? 3? or 3x something? 6? 9?
Ahh, is this the spec sheet, or at least similar?
http://i983.photobucket.com/albums/ae311/freakingstang/Kubota/Satoh S370D Beaver/c83fa4b5.jpg
So, you have a 3x2 transmission, and without third, you have gears 1,2,4, & 5 (missing 3 & 6)
How much of a pain is it not to have the top gears? On my Ford (3x3 transmission), I think I would survive without the top end as I rarely hit the high range of both gear selectors. And, while the speed ranges don't really overlap, to some extent one could skip the missing gears jumping up to the next range.
Of course, you may also not want a bunch of metal shards bouncing around the transmission, so you would want to make an effort to make sure the transmission and transmission oil is clean.
Anyway, it would all depend on how much you use the tractor. What for, and how big of a pain it is without the gear.
So, this is your tractor.
http://www.tractorbynet.com/forums/mitsubishi-satoh/276386-new-me-s373d-2.html#post3272796
It has a front end loader, 3 pt, and 4x4, which gives it some value. But, it is still a very small tractor. Does it do everything you want? Or would you otherwise be looking for a larger tractor?
I think I would carefully think about whether you really need the high end gear ranges, or you can skip the missing gears. And, whether the tractor really does everything you need. Give it a few months before you make the leap.