I’ve not worked on a Groen electric kettle in many years, but I’m VERY familiar with their competitor’s kettles. Theirs are as you’d described, whereas, the elements are sealed (welded as you put it) into the kettle.
In such a design, the elements CANNOT be replaced exclusively since they are a permanent part of the kettle’s cooking pot (that’s what I’ll call it). Therefore, entire pot would need replaced. The parts price and labor required to do so would easily exceed half the price of a brand new unit.
Your questions would get the most accurate answers by contacting Groen directly. Here’s a copy of their manual. Their phone number (888-994-7636) is on the cover. When you call them, be prepared to provide a full model and serial number:
Jimmy, can you get me a picture of the element install. It would seem to me that if they are welded in for the pressure, Groen would have a exchange kettle program. To me it’s not a big deal to remove a weld and TIG it back in place. Done it on many machines in the past. One may have to make a special cutter to remove the old weld, But with proper clamping and a milling machine anything is possible.