Except for some pre-damaged ones like Plombs with the shift lever broken off and a Snap-on with a broken tooth (vintage but still readily available part) when I bought them, I don't think I have ever needed to replace anything.
My main one was a 1962 Craftsman 1/2", HEAVILY abused with extra leverage and hammer because I simply had no other way as an penniless teenager. 100% good to go, has been cleaned and lubed a number of times but never shown any sign of trouble.
I've cleaned and lubed MANY 1940's Plombs and Snap-ons, again nothing found broken or worn out.
Ones I have had for a long time have gotten smoother and required less torque on the back swing from some combo of polishing-in and spring relaxing, but none has ever reached a point of spring tension of pawl wear that has caused a pawl to not track properly or to allow skipping. Many of these things are WWII vets that had long careers after the war.
This stuff is durable as all get out in those brands and time periods...I hardly own anything newer than the 60's. Main purpose of service has been to get out lube that was beginning to accumulate crud.
On any ratchet I like, I would BUY a kit just to have spare springs and pawls.
On the little-ball fighting types of ratchet...the Snap-on tool publicized on here has been a help, BUT if the pawl mechanism is working well, it can be cleaned and lubed without disassembly.
Soak it well enough to flush out the hole, and make sure you get some oil down that hole to prevent the spring from rusting. Also hold back the little ball on the drive square with vise grips and get some oil into THAT hole. Those springs will all out live you if you can prevent rust.