If the marks won’t wipe off, they’re likely internal. Based on the descriptions, the most likely causes are element cement separation (often called balsam separation) or internal oil contamination. Both are defects, not normal cleaning issues.

Cement separation happens when the clear adhesive between bonded lens elements starts to fail. That can create rainbow-like streaks and will degrade optical performance. Internal oil can also cause streaking and may increase flare or unwanted reflections.

Either way, this is not something you can fix with external cleaning. Repair usually requires full disassembly, cleaning or replacing affected parts, and careful reassembly. For an older 50mm lens, that is often impractical or not cost-effective unless you already have repair skills.

Yes, it can affect image quality, at minimum by increasing glare, reflections, and reduced contrast, and potentially worse depending on severity.

Best advice: if the lens was not clearly sold as defective or “parts/as-is,” return it rather than accepting it as normal.