HELP...please.... rear wheel bearing tips on installing

[Caddy Daddy]

Hi all, 8 months ago I had my rear wheel bearings replaced by my trusted mechanic who works on many USA cars, he replaced my old rear wheel bearings with ones I purchased, but within days the passenger side started to leak, for another 3 weeks or so it did, then it stopped, months passed and then I would hear the old familiar sounds of the bearing groaning, surly not, not just after 8 months, anyway that followed by the drivers side started to leak and the noise is worse and to a point as where I can hear the grinding, so no more driving. Now I have bought my new rear wheel bearings from RockAuto and had them shipped over here nice and quick, the prices were weird, starting from $7.89 to $84.99 depending on the manufacturer, kinda weird, why would you go for the cheaper one?
Anyhow I purchased the more expensive ones the SKF  RW509FR, so I hope these are the good ones, (still made in China) the others I have to get my mechanic to take out now, does anyone think I may of got a bad set of bearings? My mechanic seemed to think they come of the axles ok, and when on ok, but he though there should have another seal? Although when you look at the bearing it is all sealed, like all one unit, and the collar. So any tips for my mechanic to watch out for this time? I don't want to have to replace another set before the end of next year, I want at least a decade out of them. Any tips?
Regards Milton Watkins

[dadscad]

Early this year I replaced both axle bearings on my 63 when I replaced the differential carrier. Within 150 miles the right bearing was leaking gear lube into the brake area. Fortunately, the supplier replaced the bearing but I still had to pay, again, to have it put on.

The problem I found was, the inner seal was either defective or not properly seated in the outer bearing race. This allowed gear lube to leak into the bearing and wash the bearing grease out of the grease seal on the outside of the bearing. When the inner race of the bearing was spun, the seal inner slipped on the outer race instead of the inner race. Be sure the oil seal with the spring garter that goes inside the axle housing, is fully seated on the outer race of the bearing and does not slip there.

HTH,
David