What he said.
I'm not a gearbox specialist but sounds very very odd to me. Those seals are pretty good be hard work for oil to get in and out.
That and the fact there's just no need to leave them in there when they flick out so easily!
Also, two random things to think about- does the oil flowing through the races provide a cooling effect on the bearings?
Is flow of oil to parts of the gearbox restricted by these seals?
With regards to the origional bearings being nice- without knowing how much care they took to remove them and how tight they were on their shafts/housings they could have been damaged.
Generally speaking bearings are cheaper than the labour to access them and the other associated extra costs with having them fail. I always consider assembling something with old bearings to be bad practice. (Rambling as usual soz)