I'd not worry about it.
It's just the oil from the last and unburnt charge that has collected at the lowest point plus any bleed off from the oil injection system.

If it were an RG500 you would laugh as the infamous dodgy oil check valve issue usually leave the void behind the inner RV covers full of oil and if let stand, the carbs on the lower cylinders end up half full of uninjected oil.....

Just rebuild and fire up.
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