Firstfives.org

hi,
While replacing the blower motor on my ’77 530I, I found copious amounts of dirt and debris all over the heater core. I I’m expecting to need to pull the dash out to access the top to clean, is this a valid assumption? Once I have access, I’m going to clean the debris and use a good foam cleaner for heater cores or condensers to ensure it is fully decontaminated, maybe Toyota setup or if I can get my hands on bmw oem cleaner.

Any suggestions on the easiest route?

Pic attached of the dirt. It’s tucked way back where a vacuum will never reach