To buy heat seal Item # IF117-014-1

Is there a specific reason you thing replacing the heat sink is necessary? If your machine is running hot it might just need a good cleaning. Dust buildup, especially in older machines that have been in use for a long time, is the most common cause of poor thermals on any computer. It's also the easiest to fix. If you want to go the extra mile, you can apply new thermal paste to the CPU (and GPU). But in my experience, heat sinks don't go bad very often unless they are physically damaged.

The replacement battery is also a good idea since an aging battery can contribute to higher temps.