Hi Stuart-
I agree: “If it ain’t broke, don’t fix it!”
Unlike some of the folks here, I don’t roast huge amounts of coffee (2-3# per week?). But I do track IBTS temp vs. FC (& SC). When IBTS drifts down by about 10F° at FC I clean the IBTS which of course requires removal of the face plate. I tried using Roast Analyzer to help visualize the drift by comparing roasts from different times, but since they place the FC marker on BT instead of IBTS I have a hard time telling for sure. So I end up using the roast profile and jot down numbers. You probably know you will need cotton swabs and alcohol to clean the lens of the IBTS. Odds are good you’ll end up cleaning the rubber view port as well as it’s pretty close quarters.
Be forewarned that you will need to support the face plate once it’s loose from the roaster body. Try to catch the drum as the plate moves forward so it doesn’t drop on the surrounding induction coils & insulation (I think that’s what surrounds the drum). There is very little extra length to the wires and you don’t want to hang the plate on the harness so have the support ready.
In my case, the interior surface of the face plate accumulates a lot of smoke residue which wipes off readily; there is also oily residue under the smoke particles and that takes time to soften & remove. I’ve used dish washing detergent but would have used Simple Green if I had it.
The inside-facing surface of the glass on the hinged door accumulates oily residue (Simple Green again, or just water if you clean it frequently), but that doesn’t require removing the face plate. Cleaning the metal of the door is easier if the face plate is off. Plus you can check the hinge screws are tight while the plate is off (mine weren’t… they’d loosened a little).
I did one serious cleaning after 7+ months of use and it needed it. There is significant oily residue that accumulates if you frequently roast to FC+ or Vienna which I do. The bean temp probe and the surrounding area of the face plate had a lot of that oily residue. I don’t know that cleaning it makes any difference, but I did and there was a lot of gunk. Makes sense as that’s where the beans tumble, surrounding the probe; the movement of the beans in that area is minimal and relatively slow.
While the face plate was off I dragged a rag through the transfer tube to the rear where it would enter the chaff collector. Not sure that did anything but get the loose smoke residue out of the way. In hindsight I should have put more effort into cleaning that tube.
The housing where the exhaust fan is mounted needs cleaning more often, but you can see the contamination each time you empty the chaff collector. In my case the filter screen of the chaff collector needs to be cleaned with a wire brush every 3 or 4 roast sessions. The loose chaff is easy to vacuum out, but the oil sticks to that screen of the chaff filter which increases the pressure-drop across the filter. Again, I roast pretty dark so you may not see the same thing.
Btw, be careful when re-installing the chaff filter. There are 2 grooved edges on the rubber seal-
- One on the outside edge that is easy to deal with when re-installing the rubber seal.
- There is also an inner groove where the chaff filter mounts… that one I never noticed till I had ErC 4. I had some new beans that had a lot of chaff. Because of the limited air flow, the collector got so hot it softened the rubber seal and was literally sucking the chaff filter out of the rubber causing it to contact the impeller. Had I seen the groove before and made a proper effort to seat the filter properly I wouldn’t have had the issue of the chaff filter contacting the impeller but I would still have had over heating (iirc, ErC 4).
More than you asked for. Sorry… it was all in one chunk! 
Bruce
. I used to be a Fahrenheit HotTopper before switching on the Bullet because you all said the coffee tasted better in Celsius.