As title, 115mm 240v no matter what I buy the god damn things die within a year. It’s always the same thing, the armature starts growling bit by bit.
By Armature growling, what do you mean? When mine make a growling/groaning/screaming noise, a quick dismantle and lubricate the bush (not brushes) at the rear, possibly the one into the gearbox if it's not a ball race. Clean the old, dirty grease out and apply some more - don't add too much and pack it - you can have too much grease!
4" B&D must be 40 yr old now - admittedly not in everyday use. 115mm B&D has survived more use in the 8yrs I've had it, but again, it's not industrial use. I think one important thing is not to get them too hot from continual use -the grease running out the gearbox, or needing gloves to hold it might be an indication its getting a wee bit too warm As is letting the tool do the work, not forcing a cut.