@alpha_lam gotta disagree with you on the 'if you plan to own a supertek, be prepared for a very involved experience',.. you bought a used unit and have issues, you are in the minority of owners out there. If owning a Supra was 'involved' Mick wouldn't have a business. Especially a biz with tons of units out in the field an such a loyal following. Yes, stock units will present issues from time to time and yes when I have repaired, I have found a bad solder joint here and there, it is not the norm though and honestly they have been much older units that have had some very obvious use and been banged around a good bit. His soldering is excellent and rarely do I ever find bad joints though on occasion I will.
Regardless, it happens anywhere in this business and more importantly Mick covers any issue on stock units for their LIFETIME. That's pretty amazing considering the size of his operation. I'm not aware of him using electrolytics in the cathode of the DHT, much less anywhere in the circuit save for on PS regualtors or B+ filtering in early models. I have worked on these units with models going all the way back to 2005,.. always film caps and always one on each side of the DHT filament above the center tap. It sounds as if this unit was modded and someone didn't know what they are doing based on your description. When I repair a unit, you would be hard pressed to tell that the circuit (solder joints) are not original and had been repaired. It is entirely possible the unit was modded (which it sounds like from your description). Not to mention that when that unit left Mick's shop, I can almost guarantee that it did not have the issues you experience. That type of imbalance would have been easily caught while Mick QC'd the unit. Anything is possible so I'll stop short of saying it isn't possible, but I do want to correct you on your idea that Supra's in general require effort to own. That is just not true as they are created and made correctly 99% of the time.