Check out my signature and you'll see I drive a '94 Fleetwood Bounder, Diesel. So they did, and do, make Bounders with a diesel engine.
Hopefully your mechanic found something loose and tightened it. Maybe not. Sad but true, many, many mechanics struggle with understanding the parking brake on older gas rigs and on the Workhorse chassis so you should arm yourself with some info. I'm not sure you have the Workhorse chassis though. That's the chassis with the infamously unreliable park brake system.
We longtimers here on RV.net have gotten help from a member with the handle, OldUsedBear. Here's Oldusedbears web site that discusses the P-B system. There's contact info. He's well known here on RV.net and over at iRV2.
Web site:
Autopark InfoHope you get your problem fixed up quickly...