I use these motors with great success-
http://www.ebay.co.uk/itm/110739940158? ... 1497.l2649
they are brushed motors and draw 3A at 12v running 75mm pc fans and provide more than enough thrust for my mini rov. i'll measure it when i get a spring balance. they are fairly easily sealed as they are enclosed motors anyway. I sealed them by gluing a rubber cap over the rear bearing and using epoxy round the wires.
The shaft seal on one of mine came from a pc fan with oil filled bearings, this is 3mm id, 5mm od and fits perfectly in the recess round the motor shaft. sadly i dissected several pc fans and couldnt find another one with an oil seal so i'm using two o rings instead.
If anyone knows of a source of 3mm oil seals please give me a shout.