I primed all of the firewall areas that had minor corrosion issues, and there were very few of those, to prep for finish painting that will be done later. Spent some time cleaning up and inspecting the engine compartment wiring harness and so far everything looks very good. Need to let it cure for at least 24 hours, so I moved on to working on the blisters themselves. Overall, they looked really good and solid from the outside, but were a rusted mess internally. 
These items function to channel the water coming in from the cowl vents out of the vent system and drain that same water under the car. The problem was that they are lined with insulation that soaked up water like a sponge and just sat there corroding the parts from the inside out. As the metal deteriorated and flaked off, it blocked the drains and the bottom channels holding the insulation were rusted out completely. The metal while still intact and solid, is very thin on the bottom with some minor pinholes.
These parts will probably be hard to find in any kind of usable condition, so I will repair then either by building them up inside with epoxy or body lead. I will then re-insulate them using closed cell neoprene instead of insulating batts and with the drains now clear, we should have no further corrosion issues here. It is important that these be rock solid, especially on the driver’s side, because the brake master cylinder and vacuum booster are attached to it.
Final project today was to scrape, sand, wirebrush and prime the vacuum tank which was mounted down low in the front left fender under the heater core assembly. A curious note here was that in working with it, it appeared to have an ounce or two of engine oil in it. On the plus side, it probably means that there is little or no corrosion in it, but I’ll have to do some research to figure out why it was there in the first place.
