How do I know if my water heater is fixable or I need to replace it?

It's a gonner . . . Time to replace. Look at the date on the water heater and see if it lived past warranty.

When you do replace, hopefully you can install yourself and save a boatload of money. I had to replace mine a couple years ago and thought I would pay for installation to make my life easier - oh how wrong I was. They wanted more for installation than I paid for the water heater!!! Are they crazy out of their minds??? I had already drained the old one and unstrapped and removed it. Called one of my neighborhood pickers to haul away to be recycled.

So sorry, needs replacing.

can you see the leak? If you can why not try that tape in the commercial in the row boat (sorry, the name escapes me,)

That depends on where it's leaking from. If its leaking from a rusted-out spot on the bottom, then yes you need to replace it.

A water heater leaking from the bottom is not always an indication of tank failure. Before you resign yourself to replacing the entire water heater, take a few minutes to determine where the leak is actually coming from, and you may be able to fix the leak yourself with little or no cost.

The first places to check if it appears that you have a leak from the bottom of your water heater are the drain valve and temperature & pressure relief valve (T&P valve).

On most water heaters, the pressure relief valve is on top of the unit, but most systems include a tube attached to the valve in order to channel the water to the floor. When the T&P valve is leaking, it may appear the issue is at the bottom of the tank since the overflow tube discards the expelled water underneath it.

Read more here:

https://www.waterheaterhub.com/water-heater-leaking-from-the-bottom/

Some states mandate installation by a registered plumber. You may research the brand reliability in advance, but if you are required to have an expansion tank, note that new sizing may change from that which you currently own.