You may have two vents, one under the driver's left elbow hidden under the sheet metal just above the rear axle. Other at or near hyd fluid fill port.
Cheap plastic, looks like question mark per prior poster. Mine just slips off the tiny barbed nipple sticking up from the xmsn housing. Easily lost and when correctly placed doesn't seem to last long before rotting. For mine the local dealer price was something like $18.
Dirt daubers love these things; around my area plugging is common.
I replaced mine with a short piece of thick-wall fuel hose and a U-shaped piece of 1/4-in copper tubing mashed almost flat in a vise then wrapped the thing with a layer of fiberglass netting and cable-tied it. Don't need a big hole, a tiny vent that stays open works fine. Use a small hose clamp to hold the fuel hose onto the nipple and another clamp to hold the copper from slipping out of the fuel hose when it gets a bit oily.
Please post back and advise your experiences and how resolved this problem so we may all learn.