Well, I can't imagine how, particularly if that was water in the cases, but I think you may just have struck lucky.
There looks to be no damage on the shaft which would indicate a failed bearing.
The grooves won't be from the seals ... there is hardly any relative movement between shaft and seals so wear is unlikely.
That's one reason that I suspect that damage on assembly is common, since failure is fairly common.
I would normally tend to change bearings as a matter of course but, having had recent experience of just how difficult these are to replace and, bearing in mind (sorry) that this is an isolated system where failure will not have knock-on effects to other components, I would be inclined to regrease them and put it all back together.
I would just change the outer seals.
If I remember correctly, the grease spec calls for black, molybdenum disulphide grease, which is what I used.
On another tack .. I notice you have budgeted for new half-rings for the valve stems.
Are you aware that these acquire little "bedding in" grooves which will mean that if you fit new ones (or refit the old ones upside down) the valve clearance/s will all close up by approximately one shim size.
I bought a full set, intending to change them .... 15k miles later they are still in the bag.
Have a look at this thread.
http://www.ukmonster.co.uk/monster/s...ht=valve+shims