Gas Range repair question (DIY) - tube manifold supply


Hi all:
We have a 3-4 years old Kenmore Gas Range (purchased from SEARS), the model# is 362.73221200 (or 73221 for short. Here is how it look like: http://www.epinions.com/pr-Kenmore_73220_73221_73222_73224_Kitchen_Range ). For some reason the oven knob is starting to get wiggly. So we took out the knob and found that while the knob-thermostat is OK, the "switch" (officially should probably be called "Tube Manifold Supply") is loose and wiggly. I think it might need to be replaced. Luckily, we still keep the original "Use and Care Guide" as well as the "Repair Parts List", and I took a look at them and I think the part number is WB28K10109. I then did a search on Google and was able to find this part for $29.95 (see: https://secure19.nexternal.com/shared/StoreFront/default.asp?CS=yemma&BusType=BtoC&Count1r0501124&Count2c7641549 ).
Here are my questions:
1. For those of you who are experience in gas range repair, is this (tube manifold supply) usually go bad after few years? Would replace this part fix my problem, or there might be some other hidden problems that need to be fixed? Is this something that I (a typical family handyman) could repair by myself or really need a professional? We found a SEARS technician to give us a price quote and he said the part would cost around $100 and the labor would be $135, so total he will charge for $235. With a new gas range, we probably only need to pay $299 (install and haul-away included, from homedepot.com), so it doesn't make sense to us. But as this range is only 3-4 years old (and all the burners are still working great), so I thought that maybe I could get it fixed by myself to save $$$. What do you think? Should I go ahead to buy a new one or should I try to fix it (we purchased it for like $549 or something, can't remember now)
2. I had trouble to find out how to to "life up" the cooktop. Any idea? After lift up will I be able to directly acccess the tube manifold supply? thanks!
Thanks in advance for your help!
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Sorry there was a typo, I meant "lift up" not "life up"...
Any help would be highly appreciated. Thanks again!
T. T. wrote:

https://secure19.nexternal.com/shared/StoreFront/default.asp?CS=yemma&BusType=BtoC&Count1r0501124&Count2c7641549 ).
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<% } %>
<%-name%>
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