As mentioned in the linked thread in my earlier post, good-luck finding the exact 100K trimpot with the extended white knob. I do not see any manufacturer part number or markings on my 153IR.
But if you're determined to effect a DIY repair, as I suggested earlier you could simply insert a generic 100K trimpot that would not have the extended knob. I showed an example of such a 10 cent trimpot and a listing from eBay. It would require some soldering finesse to attach the 3-terminals of the trimpot to the 3-holes in the circuit board...not to mention removing the existing 3-terminal trimpot which can be a hassle without steady hands and the eyesight of a teenager. 
The 3-holes are on a "standard" 5mm x 10mm grid for which it's easy to find a trimpot that would fit. For example for a bit more you could use this 100K trimpot from DigiKey (US distributor). Note that DigiKey shipping will be $4-5 so you'd end up paying more for shipping than the parts themselves! No extended knob so as shown in previous post you'd have to poke a screwdriver into the case hole to adjust the trimpot...but you'd only need to do this once.
On the other hand, how about this. If you look at the board and feel confident extracting the existing 100K ohm trimpot, why not just replace the trimpot with a fixed-value 5-cent resistor. I believe you said you're just looking for a 30 sec delay which I believe is about half the maximum settable delay of 1 minute. If this is the case then just insert a common 47K resistor (about half of 100K) across 2 of the 3 holes and you'll get a fixed (i.e., non-settable) delay of something close to 30 sec. I don't know if you have an electronics DIY buddy or an electronics store (like a Radio Shack equivalent) nearby but it is easier to find a 47K resistor than a 100K trimpot.
