Here is some photos for heater's upgrade ( 105's). The heater came up from a berlina 2000 '74 model. I replace the old motor with another one restored, clean and paint the core, ckecked the valve ( puting a new rubber gasket, too, de-rust the flaps (then covered the metal parts of the flaps with special protection sealant) and lubricate all mouving parts with lubr from Wirth brand.
After looking carefully at the heater itself and the way air is coming in (and of course some dust, stones etc) I realized that the system suffers 1. from the air inport and 2. if it happens the water came in, or have a leaking core, stays always at the bottom, exactly where the motor lives. Main reason for motor problems is this.
For the 1. I put an aluminium thin net in front of the air input, to eliminate the coming of the hard and bigger objects. At least, even in case those are there, must staying outside the heater.
for the 2. Just drilled some small holes at the bottom of the heater. A very nice idea for the luna DIYer, might be having only one hole, then pass a small silicon hose with a small valve at the end .In case there is unwanted water there, you will open the small valve and make the water come out. This will be hidden behind the heater, it is easy!