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I've seen bad crank seals on motors with little and even no hours....Ones that have sat without running. Film of oil on all metal parts...They are OK. Rubber is kind of 'living' and needs the oil pushing 'against' it (into the microscopic pores of it even) to keep it from dry rotting out. In most cases I'd roll with Juliend's experience as well, but I've seen otherwise also. I blew up a NIB unfired Italian kart motor the first time I ran it because the seals aged while it was in the box. Only rubber part on the whole motor...These things are literally like 20 parts total...Two of them being crank seals...LOL. I've thought more than once that 6oz or so of SAE30 poured into a tubeless tire of a vehicle that's going to see low use would wane off dry-rot for a lot longer. We've all seen tires that rotted out before they wore out.

I'm now about to mod my spare motor to replace crank seals a bit quicker, does anyone any previous evidence of this being done or am I to be the 1st to record it?

It's been done. Have the "tabs" machined off, drill and tap holes for some bolts to hold the new "retaining" plates that you build on.

I'm currently dremelling the retaining tabs off.

Do you know exactly where the threads were put and what size bolts? The most meat is on the section that holds the seal, I was thinking of using 3 M4x7mm bolts and using a large washer with 3 holes driled in to act as the seal retaining plate.

Sadly I stripped this spare engine a few months ago and I can't remember how much clearence there is here.

is it not possible for seals to dry out over time when the bike has not been ridden and oil type standard oils are all petro based witch in time will degrade rubber plus addatives seals dry out.... not a bearing issue sure if it in your means to replace both go for it but not always necessary