I have a Stihl 036, 25 years old. Still starts and runs like when it was new. I had trouble years ago probably related to alcohol blended fuel. The original fuel filter stone disintegrated, filling the carburetor with fine residue, requiring disassembly and cleaning. The carb is a fairly simple aluminum cube, and the settings are fairly simple, laid out in the manual. It's running on it's second spark plug, but probably due for a new one.
The air filtration isn't as good as the Husqvarna centrifugal system by a wide margin, but quite adequate. I carry a plastic brush to clean the sawdust off at refueling. The original flock coated air filters were problematic, as the flocking is delicate and would wear off, allowing debris to pass the filter. I recently replaced the filter, now Stihl uses a fine stainless mesh instead, that will last.
I always use the brake on my saw, and to date it has required no attention. Not employing the brake, or disabling it is amongst the most dangerous things that could be done. Really a person shouldn't even take a step without the brake applied, a chainsaw should be considered safe only if your feet don't move. Cleaning brush is good practice, but in practice it's impossible to safely clear all tripping hazards around trees. You certainly will trip now and then, and probably on the most insignificant things, so I see it as just minimizing the consequences.
As for bucking up logs, cutting over snow is great for providing safe clearance. I also agree generally with what Steve says. I also like to bend over and cut fairly perpendicular to the ground, but if you have a good sense of where the bar tip is, you can cut pretty close to the bottom without great risk, and generally one cut somewhere should be right through, then you can kick the log over a bit, and safely complete the other cuts.
It might be over cautious, but I like to blend the fuel at 25:1, rather than the 50:1 they recommend. I feel it gives a wider margin of protection, and doesn't seem to cause plug fouling. It does seem to serve to repel mosquitoes...