Hello,

I am not sure if this has been discussed before.
We have a "Hell Hole Inspection and Rustproofing Hole" on our cars.

I found out while viewing pictures of NOS sheet metal from other members in this forum.
Close to the rear trunk cross panel hidden under the big round plastic covers there is a rather big (Ø20mm) hole on each top side of the longs. Perfect for viewing with a probe and for rustproofing. Reaching down all the way to the bottom underneath the infamous hell hole. Enclosed are some (poor quality) pictures of my 71. Makes me happy to see almost no rust here.

Cheers, Arno

I bet the people who didn't know about this are probably going out to look at their cars...

I just did, yes the holes are there. I'm sure they will come in handy
Thank you!

go deeper

Now that you know about the hole, you can "accidentally" drop extra hardware in there. Ask me how I know.

Thanks for the tip Arno, is there a recommended rust proofing agent for coating the insides? my gut tells me an light weight oil based product

The little british car world uses waxoyl. Mineral spirits and wax judging from the smell. #M makes a spray can version which seems a bit more sophisticated by the smell and appearance. The top part of the long rarely rusts. Get a boroscope camera and drop it down to the bottom. They are now pretty cheap, and some of them are waterproof so you can swallow them - a go figure sort of thing.

I lot of us use Eastwood internal frame coating but I always follow up with 3M Cavity Wax Plus (equivalent to waxoyl). I think cavity wax is superior to the frame coating so if I were to only use one, I'd go with the wax. When I pulled my car apart for resto, areas I had treated with cavity wax 30 years ago looked pristine compare to untreated adjacent areas that were riddled by tin worm.

I had my car treated with cavitiy wax some 30 years ago (thankfully). The waxed areas still look like back then.
For many years now I use "Fluid-Film" on all of my cars for protection of the cavities. It is a rather thin liquid based on natural oils and tends to creep for a long time. On my almost 30 year old BMW E30 there are no rust issues despite driving all year round with some salt on the road during winters here in Germany.

Anything oily, greasy etc. will do good + regular cleaning of the underbody (remember all the grime and dirt collecting around the 914 jack posts?)