• Here are a few options
• depending on how formal or informal you want to be
• and the exact nature of the "mark": 1. **Una pequeña mancha en la parte trasera del hombro derecho.** * (A small stain/mark on the back part of the right shoulder.) * *This is probably the most common and natural way to say it.* 2. **Una pequeña marca en la parte posterior del hombro derecho.** * (A small mark/blemish on the posterior part of the right shoulder.) * *Slightly more formal
• "marca" can be used for a general defect
• "posterior" for back.* 3. **Una ligera imperfección en la espalda del hombro derecho.** * (A slight imperfection on the back of the right shoulder.) * *Uses "imperfección" for a general flaw
• "ligera" for slight
• and "espalda" for back.* I'd lean towards the first option as the most straightforward and widely understood in South American Spanish for a defect description.

Características:

• Etiquetas oficiales y originales de Nike adjuntas