Chainsaws

I have a 55 chainsaw (EPA). The label on the side of the housing reads: 967 05 27-00 and 99 1201905. When I am searching for parts, none of these numbers match the serial numbers, etc.

Question1: Which, if any of these numbers is the serial number? If none of them are, how do I find the serial number?

Question 2: I have had trouble with the decompression valve - it won't automatically close after the saw is started. Its been changed many times. I'm thinking that maybe the wrong replacement valves have been installed, with no solution to the problem. What is the correct decompression valve part number for my saw?

Question 3: The Operator's Manual I got with the saw is called 51/55. In looking for information I sometimes see reference to a model 55 Ranch. I assume that my saw is not a 55 Ranch. Is that correct?