Model number is on a tag somewhere on the appliance. It reasonably should be viewable without uninstalling the unit. Does the cooktop raise up? May be beneath there. May be on the frame of the oven cavity or on the door.

Part number sometimes is molded into the knob.

Clean up the knob with alcohol - let dry. Get some JB-Weld at the hardware store - you can make that knob work like new.

Is this it?

http://www.ebay.com/itm/Genuine-189100-Thermador-Cooktop-Knob-SGS-X304-Rear-Black-/252507636823?epid=1964502031&hash=item3acaa0c457:g:DFAAAOSwSlBYwfX7

I usually use www.repairclinic.com but most of what I saw with your oven model number is no longer available - but then I searched eBay on the part number that repair clinic provided...

I too have the same problem and from what I can tell, we are out of luck. I have been in need of 2 knobs for over a year and periodically scan the internet looking...just as I am today. If I find anything I will let you know and please, please, do the same for me. It really is a shame that for what we spent on these ranges, Thermador isn't of any help. I have the vent and a dishwasher and cringe thinking I'll have the same issues.

They make generic knob kits for ranges. You can google them.

Your model number is rdds30. Knobs is part number 00415364 or 415364. I get those sometimes and sell on eBay. I also have many other discontinued thermador parts. Lance. Dr. Frankenstove. 978-888-1000

If you still need any parts, I have this range and I can sell you any parts you need as I am no longer using it.

Hi Giffney can you sell me the conversion for gas LP of you Thermador RDDS30