3AG does NOT mean a fast acting fuse. It could be either fast or slow blow. The 3 means it's 1 1/4 " long, the "A" means it has Axial connections, and the "G" means it's made of glass.

See https://www.ebay.com/itm/195167031668

What brand is your smoke detector?

Why bother with the extra middle section? You just need to smooth out the damaged parts and connect the two ends. The extra section is a bit redundant.

This is a faston connector or terminal. Sold at Amazon.

Use Google and search for Locking Pin.

You can purchase it at almost every hardware store.

At the top of the guide, click on the link at Parts.

Both ethanol and isopropyl are very suitable, although isopropyl will evaporate less quickly and leave less residue. Ethanol is often used to clean glass, while isopropyl is more often used in the production of electronics.

relay

Look at the top of this guide at Parts