Your question appears to be based some some incorrect premises. Many things can be repaired without looking like a stitched or glued together Frankenstein-like patchwork of parts. Transporter/replicator technology alone would allow his skin to be repaired fairly easily without leaving visible scars.

Secondly, Dr. Soong took great pains to make Data human-like down to the smallest details. This is why he's able to eat and drink normal food, breathes, blinks (based on a Fourier series), is anatomically correct, has an aging program, has hair that grows (at will), and is even able to dream. It's therefore likely that Data's skin also self-repairs to some degree like a human's, and there's no evidence that it doesn't.

There are no canonical sources describing Data's skin, but a close-up of his hand shows that his skin (Data refers to it as molecular fabric; in a later episode, it's described as bioplast sheeting) has a cell-like structure:

Lastly, there's no rule that says only carbon-based materials can be self-repairing. Here's a clear counter-example.

I would assume that Data's skin is probably resilient enough to resist fatigue at his joints, or the bioplast sheeting has some basic self-repair functions to counter deformation stresses. When his skin does need manual repair, it would be a simple matter of grafting new bioplast sheeting over the damaged area. If a dermal regenerator can heal wounds without leaving scars, then how Data's skin can be repaired without scarring should require no further explanation.

Your question appears to be based on some incorrect premises. Many things can be repaired without looking like a stitched or glued together patchwork of parts. Transporter/replicator technology alone would allow his skin to be repaired fairly easily without leaving visible scars.

Secondly, Dr. Soong took great pains to make Data human-like down to the smallest details. This is why he's able to eat and drink normal food, breathes, blinks (based on a Fourier series), is anatomically correct, has an aging program, has hair that grows (at will), and is even able to dream. It's therefore likely that Data's skin also self-repairs to some degree like a human's, and there's no evidence that it doesn't.

There are no canonical sources describing Data's skin, but a close-up of his hand shows that his skin (Data refers to it as molecular fabric; in a later episode, it's described as bioplast sheeting) has a cell-like structure:

Lastly, there's no rule that says only carbon-based materials can be self-repairing. Here's a clear counter-example.

I would assume that Data's skin is probably resilient enough to resist fatigue at his joints, or the bioplast sheeting has some basic self-repair functions to counter deformation stresses. When his skin does need manual repair, it would be a simple matter of grafting new bioplast sheeting over the damaged area. If a dermal regenerator can heal wounds without leaving scars, then how Data's skin can be repaired without scarring should require no further explanation.