After Seafoaming the engine, the spark plugs were replaced.
After removing the old plugs, cylinder compression was checked again to see if Seafoam made any difference. Not much; the numbers are perhaps slightly higher overall:
Cleaned out the spark plug wells in the cylinder head with cleaner and a rag as best I could.
The 5/8″ (16mm) magnetic swivel spark plug socket by Gearwrench (in photo) is great! I like the captive extension and magnetic feature a lot.
Used genuine Volvo plugs which are fairly expensive, although there is vigorous debate about which plugs to use. Seems the consensus is that Volvo plugs are best so I went with that. These appear to be platinum- or Iridium-plated plugs with triple ground electrodes permanently gapped. Compared to original single ground electrode copper plugs:
Put all five new plugs in
And tightened to specified 18 ft-lb torque
Fired the engine up and it runs smoothly.
$24.32