What do you mean with "valve rings"? Do you mean piston rings or valve stem sealings?

Due the stem sealings do not affect the compression rate, I presume you mean the piston rings. In that case they're OK, as you stated.

That means it's either stem sealings or it's a oil pan ventilation, which is maybe clogged by water/oil emulsion because of many short range trips with cold eingine.

Valve stems will hardly make the spark plugs wet, so I'd take a deeper look to the bottom of the oil cap and if theres some sludge I would inspect the oil pan ventilation.