Synthetic grease can get liquidy from being used with dino sometimes. My experience is that the dino liquifies the synth wherever they come in contact. So it's important to thoroughly clean any trace of dino out of the bearings if you switch to synthetic. I use brake cleaner spray liberally on everything, until the surfaces and bearings are bone-dry, and I inspect the bearings very carefully for any hidden deposits of dino grease. The stuff is good at hiding on the ends of the rollers and inside the creases of the carriers.

The runny grease you're desribing sure sounds like that's what happened. If you overpacked (sounds like you did), that would have forced the thin stuff right through your seals. Kind of like making a drink in the blender with a loose lid...&^)

You shouldn't need a second seal back there if the spindle is good and the grease stays thick.

A couple things:

1) Perhaps you overpacked them...I tend to think like you though "more grease can't hurt"....but you must allow for thermal expansion and mechanical displacement.

2) I have seen some cheap, so called synthetic grease get very watery and separate...sometimes just sitting there.

3) Most greases don't mix well with other types of greases....was there other grease remaining?

Sounds to me like you over packed the hub. When filling the hub with grease you only pack the outer area between the bearings, leaving a hole through the middle. You don't pack the outer cap either. Just grease the bearings in the palm of your hand, nothing excessive.

With a taper bearing it is also important to set the bearing correctly. The Volvo method is slightly odd in that you torque up the bearing and then back off the nut, can't remember the torue setting. Basically when you have set the bearing you should be able to twist the washer behind the spindle nut with your fingers, tighter than that and the bearing will run hot

Regards