and then search for 2GM20F. Please note that some spares are different as to whether the engine is the Japanese built version or the European built version (YEU prefix on engine number.)
I've had a niggling air leak on my filter bowl since new, and have at long last replaced the horrid skinny little Yanmar O-ring with a 45mm o.d. x 2.5mm section dia O-ring from www.polymax.co.uk - thanks to Cliff for the link ages ago. I'm now looking forward to tackling Portsmouth Harbour entrance without that horrible feeling in the pit of my stomach.