Gpz550 lower compression on #1 cylinder

Hi,
i measured thecompression a while ago and all 4 cylinders had 170psi.
Yesterday i tested again and #1 cylinder has only 120-130psi.
When adding oil it only gets 10-12 psi more.
The valves are in spec. The headgasket is leaking a bit, also the base gasket so i have to open it anyway.

Engine starts and runs normal and the plugs look good and all 4 the same.

What could this most likley be? Valves not sealing good anymore or worn or broken piston rings?

Regards David

The headgasket is leaking a bit, also the base gasket so i have to open it anyway.

the 550's are bad for oil leaks: high oil pressure and mimimal top end oil feed channel gasket area. Oil leaks and compression leakage aren't always related.

When did you run it last? Engines that have been stored often exhibit sticky rings and I don't pay too much attention to compression figures until the engine has been run for while.

Your 'wet' test, if not improved soon indicates valve or head gasket problems though. Try retourquing the head when cold to the correct factory manual sequence for starters.

I ran it all the time. Last week a couple times.