My experience with terrafirma shocks and springs would say there no where near as good as ome stuff. Springs rust massively quick and shocks snap pins or leak fluid from new. Had 2 sets of terrafirma shocks replaced under warranty before ditching...
Remove the swivel seal and let grease drip out. Refit seal and fill with new grease. Make sure to turn the wheels so new grease passes the goes into the swivel and not on top of it.