Double check the flametrap element. They don't take long to plug back up on an old engine (especially the ancient waffled copper design, no longer used on your 1992, but someone could have put one in later as they can still be found). Also check the little hose PCV brass port on the throttle body (you can remove it and carefully rod it out with a small drill bit), but there's almost no way that should cause your plug to blow out. You could also double check your oil box by blowing back through it with the oil filler cap removed, but I'd be very surpised if a relatively new one was plugged again so soon.

To confirm that it may be excessive crankcase pressure, you could check for evidence of oil leaks at the front engine seals (cam, auxiliary shaft, crankshaft) collecting at the bottom of the timing cover. Failing all that, I'd just put the strap on and wait for further evidence.

There's always the chance it's the beginnings of a blown head gasket, but again I'd wait for further evidence. The oil on the dipstick and under the valve cover looks nice and clean, not at all milky? Unexplained coolant loss? You could do a compression leakdown test if you remain concerned.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now