Thank you for sharing this, it was very helpful in my research with working on figuring this out. I would be interested in knowing what the part numbers are on the semiconductors and that IC to help confirm some understandings I have. Your question about what was on top of the heatsinks, the three components wired together, those are bridge rectifiers that he is only using half of the diodes on the positive side in parallel instead of one big diode to protect the electronics from being hooked up with the polarities reversed which will cause damage to the panel and electronics.He was in the audio electronics business for decades and probably had a big box of those bridge rectifiers to use instead of spending a lot on one large diode in the beginning, but you can see in one of his videos they eventually used just one large diode instead. Your other question was about the brown stuff on the terminals and if that was from over heating. That is just left over soldering flux from when the buss wires were soldered on, it is completly normal to see in electronics and has nothing to do with over heating of a heat sink like you think.

Here is a video by the manufacturer (Tesla Chargers) explaining how these charge controllers work and what makes them different from any other solar charge controller on the market: kzfaq.info/get/bejne/a5yJeKmUqcDSXWQ.html and another video explaining what all of the components on the inside are: kzfaq.info/get/bejne/r59jfNqZtK27cmg.html

How good has the unit worked so far?. Any updates for us?.

thats a rough a***d way to use (40 amp) bridge rectifiers... the're made for ac to rectification and it looks in that setup they are using them as blocking diodes with 2 of the 4 diodes in each pack being wired in parallel, and then 3 packs in parallel , so you effectively have 6 diodes linked up. But... they heat figures and amp ratings are not for continuous dc steering, so they may be getting a little warm, the staining you can see on the solder is from where they have got so hot the flux in the solder came to the surface. they should be using schottky diodes,.. the gubbins on the sides of the heatsink are no doubt ''mosfet switching transistors'' to regulate charge / cut power / on / off etc

It will be interesting to see how it performs in the long term. I don't think your batteries are being boiled to s#*t but keep an eye on the fluid levels if they continue to slightly bubble all day. One thing that is particularly good is that components in the controller can be easily replaced if anything goes wrong. A local Radio & TV guy should be able to easily handle that should the need arise. MPPT is seriously over-rated. It has the most effect when you get a cool sunny morning and the batteries are particularly low. Contrary to the commonly held belief, MPPT has no real advantage on cloudy days, as the maximum power point voltage of a solar panel becomes close to the ideal battery charging voltage anyway.