Nothing wrong with fix over replace, but in all honesty you have been lucky. It's not always a case of needing to replace a diaphragm or valve plate. As emissions have tightened the small passages in these small carbs have gotten..... you guessed it, smaller and easier to obstruct. Spraying with a can of carb cleaner isn't going to fix that in all cases tho it will destroy the diaphragm and valve plate in short order.
Issues like a leaking shaft seal, a leaking welch plug, or check valve need to be tested for to find. To correctly diagnose a carb issue you need special tools and to properly repair one you need additional special tools. Now, I can diagnose a carb with a simple pressure/vacuum hand pump in 3 steps to decide if it is even worth touching a screw driver, but repairing any of those faults or fully diagnosing issues requires other things.
To be fair you can buy a Walbro rebuild kit online for under $10, tho I honestly have no idea how they can be sold for that since I can't buy them that cheap being a multiple brand dealer/repair shop through any of my distributors or directly from Walbro. Now, if you disregard the value of your labor and it works you get a great deal.
The average replacement carb costs between 30 and 70 dollars, add the cost of labor at any legit shop up here at $80/hour or higher where you get 10-15 minutes to diagnose the carb is the cause and (again with some specialty tools and knowledge) there are no other issues with the unit it belongs on like leaking seals, gaskets or piston rings.
Now, rebuilding a carb lets say is 30 minutes billable labor. That's $40, plus the carb kit which is realistically $15-20 and you're already into the average cost of a replacement never mind the real possibility the cleaning you did didn't get the passages open and it still may not work. Or that the metering valve seat in the carb body is worn and won't seal even with the new needle you just put in. Or that the main check valve is leaking causing poor idle not a blocked passage.
What if a welch plug is leaking - possibly because the sealant older carbs used breaks down from ethanol over time. Both Walbro and Zama used to offer special tools to remove and replace welch plugs and both stopped because it's not cost effective to perform that repair. And before you say ultrasonic cleaner will fix it, the check valves in these carbs don't normally respond positively to that with a high probability that the main check valve will dislodge and fail post cleaning. Same with high pressure air blasts to blow the obstruction out.
Stihl requires me to test certain things for a warranty claim. If a carb fails that 3 step vacuum/pressure test and I verify the fuel quality/age/ethanol % and mix oil are all Stihl needs to ok replacing the carb. Not rebuilding, replacing because the cost versus labor to rebuild/repair is better to replace.
