I am working on a similar repair on my 129 sl - I am replacing a leaking evaporator. Of course, when I ordered the parts they suggested I replace the heater core also so I would not have to remove the dash again, so I bought that, a new dryer and a new expansion valve. Anyway, I could not find any information on removing the dash, etc - my factory repair manual barely even shows where the parts are located. I bought a subscription from www.alldatadiy.com for my car - only $25 for the year. It shows how to remove every component and gives pretty detailed instructions. You might give them a try.