Changed the plugs today in my 3.0 Mercruiser TKS and checked compression. Getting 160, 135, 95, 145. The low compression in cylinder 3 is concerning. Cylinder 2 is also lower (approx 15 psi) than the last time I checked compression. Boat runs good but sometimes is difficult to start. From what Ive read these motors are known to to have rough starts? Should I be concerned? Does this sound like a possible head gasket? Thanks.