

I banned everyone from sitting on that seat until I'd fixed it, as I didn't want it getting worse. I looked online at various leather repair kits and they seemed to take two forms: either gluing a patch underneath the tear, or smearing some sort of sealant over the tear.
My cousin Di said she'd successfully repaired a tear in a leather sofa by combining the two methods, so that's what I decided to do. I ordered two inexpensive repair kits on eBay.

The first kit is basically just a piece of fabric and some glue, to stick underneath the tear.

I cut the fabric slightly larger than the tear and then used tweezers to stuff it underneath the tear. Then I squirted glue all around the edges of the tear.

The instructions said to heat with a warm hairdryer for 5 minutes and then leave overnight, so that's what I did.

Here's what it looked like the next day - you can just about see the patch through the tear.

Then it was on to the second kit.

It contained a bunch of little pots of coloured gunk, another empty pot for mixing, a thin plastic tool, and a few squares of things stapled together: practice vinyl, fabric for backing tears, and texture sheets.

I mixed my colour directly in the brown pot of gunk. I just added black and loads of pink (?!) to get the right shade, keeping in mind that it would darken slightly on drying. Then I used the plastic tool to smear some into the tear. It was runnier than I'd expected.

The next day it had dried and shrunk down.

I kept layering more gunk into it and letting it dry overnight each time. Eventually I accepted that it would never look flawless and it was good enough. (Sorry for the blurry photo!)

It did look a little shiny though, so I rubbed it with a nail file.

You know what? It's really not perfect. Fact is, there was a tear there. But at least now it's mended and we can use that seat of the couch again. We're pretty happy with that.
Here's how it looks now - if you knew it was there you'd notice it but most people don't inspect sofas for repairs so it is mostly unnoticeable.

Here's a close-up of the above picture.

Total cost for mending our couch: $27 (US$22 / £14.50). I can live with that.