New to site myself. I'm a professional handyman, which simply means I get into just as much trouble as a hobbyist, but I charge people to do it. *stupid grin*
On your garage opener gear replacement; BEFORE you tear it apart and attempt to replace components, make sure you have figger'd out WHY the gear stripped. Otherwise, instead of an old stripped gear, you will now have a new stripped gear. The most likely culprit is binding on the door's upward travel. This is usually caused by:
A.) Worn out/broken wheel(s)
B.) Worn out/broken, original imbalance of tension in the lift-assist springs (remember, the door opener DOES NOT lift the weight of the door). This applies to both extension and torsion systems.
C.) Misalignment of the tracks (settlement, physical trauma, improper original installation
D.) Improper original alignment of the opener track, causing increasing frictional wear as time goes by
E.) A foreign object somewhere in the tracks, both the door tracks AND the opener track
F.) Binding of one or more of the door hinges
Add'l food for thought - if the opener is old, consider replacing the whole thing. It's been my experience that the very second you repair one component or aspect of an older opener, invariably something else goes South - motor windings, switch assemblies, bearings, etc.
A word of caution here; if your system uses torsion springs (horizontal, mounted accross the door opening) DO NOT attempt to adjust/replace them, they are notoriously dangerous. Yes, there are instructions out there for DIY'ers, but if you've never worked on them, it can get very scary, very quickly. One mis-application of a pair of visegrips or winding "sticks" and BAM!, you're in the E.R., spending money you should have given to some fool like myself.
Just some suggestions based on a few years of breaking other people's garage door openers and then charging them for it. *really stupid grin*