I wonder if the seals were put in correctly? There are two – the inner one seals against oil and the outer against water, so they face in opposite directions. The springs should gave away from each other, so the spring on the oil seal faces inwards and that on the water seal faces outwards.
There are two large O-rings sealing between the propeller shaft assembly and the lower sail drive housing and these should be replaced when removing the shaft assembly. I replaced mine but the old ones looked fine.
Most probably your issue is the first one above. Otherwise – long shot – is your drain plug properly sealed? It is best to use a new O-ring every year. I use a tiny amount of Blue Hylomar too.
A pair of new shaft seals, a pair of new big O-rings and the drain plug O-ring cost between them under a tenner. With the boat lifted it is not difficult – though it can feel daunting – to change the lot oneself.