It takes Model and Spec Codes plus a Manual to adequately troubleshoot. I know that for the 4KY, a slightly larger genset built along the same concept as the 28 series, the Oil Switch was discontinued after a certain Spec Code. People with later Spec gensets spend a lot of time looking for a device that's not there.
Just for what it's worth, we had a gummed carb on our 4KY. I could start it, and it would carry a load until the load dropped off. For example, I could start it, turn the A/C on Max Cold, and it'd run that A/C for hours. You could hang meat or ship flowers in that coach. As soon as I reduced the thermostat setting so the compressor dropped out and the load became only the fan, genset would quit and not want to run again till it had cooled.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB