Trailer axle seals short life

[t700]

We have a 53' 2007 Utility reefer.
The trailer has super singles, which we like.
A new axle seal will only last about 6 or 7 month, so with the 4 axles we are replacing all the time.
The axles have the Stemco single nut system and when we replace a seal the Stemco procedure is followed.
Were using Lucas hub oil, but for the last 2 seals switched to synthetic 75-90 which have not leaked yet, but has been only a couple of months.

One guy we know packed bearings with grease and changed end caps and according to him has not had any problems.
I have heard that changing to grease can be hard on the spindles.

Suggestions would be greatly appreciated.

T700