Delving into the construction of seals could become a large posting site as there are many - and I mean many different types and for models I would employ the keep it simple method. why/
a too tighter seal will drag on the shaft, cause the shaft to have a wear line (yes rubber will cut into steel etc)
a miss aligned seal will as above but would fail quickly at the tighter point
From reading the postings I think most of the models seem to use a 3mm or 4mm shaft with a tube to match having brass or nylon bushes at each end fitting a greasing port to the inner end would aid filling with light grease (I use spray chain lube) and as "we" all seem to look into the vessel at the end and the beginning of each use why not top up this grease then, both as a lubricant and as a water flushing agent (to stop corrosion if the model is lay-ed up for any length of time).
I know that the SUB mariners amongst us have a different view on things and I think (I'm not sure as I don't use a sub) that they employ a total seal system
this is just the ramblings of ME and my thoughts
Richard,