This all looks like interesting and objective data, but getting down to the nuts and bolts, as someone with a 2018 GTI with IS38 upgrade and all accompanying modifications, what do I need to buy? My car just recently started to puff a little smoke upon starting, which is starting to worry me, I'm not going to lie. Car is at 102,500 miles and I don't want to start dumping in thousands of dollars. Don't know if this matters or not but ever since I had a shop do a carbon clean and water pump replacement, there has always been a hint of coolant smell, with no visible leaks under the car. I just recently, roughly 6 months after said work, had my first red check coolant level warning. I don't know if its coincidental to the new smoke, but it has to be something. I've noticed no oil loss, or at least large amounts on the dipstick. Car is rough at idle, rougher than normal, even with EQT grounding wires, OEM RS3 coil packs, and Denso IKH24 plugs gapped to 0.24. I will take a video early this morning so you guys can see. I monitor often with the Accessport, and will get 1 or maybe 2 cylinder misfires at startup/idle. I have never seen smoke during driving, however, and also to note, the car reeks lately, exhaust-wise. So much that upon starting I need to quickly put on the recirculate so my passengers don't get sick. Sorry for the long story, love the car, don't want to spend $40,000 for a lesser new car, yet don't want to start down a rabbit hole with this one, if you understand my concerns.