Yes ~ that's why they put stiffeners on later frames & much larger stiffeners on the S type. To maintain frame pressure against the door rubbers.

 

Geoff,
I had very similar symptoms as you with my Mk2 brakes. I first suspected the anti-creep system and when I found all 4 wheel hubs to be warm then I decided to replace the brake servo/booster following advice from the forum.
I contacted Barrett in Holland (distributor for Germany) who gave me the options
- recondition the original unit in the UK, but unsure cost and complicated with customs since Brexit
- replacement unit with increased ‘power’ ratio 4.25:1, but not plug-in compatible. I researched and suspect this includes modification of the cowl cover in the wheel arch. Part LR18230. No fitting kit.
- replacement unit with same power ratio 3:1, also not plug-in compatible. Part LE10117. Includes fitting kit.
I bought a replacement with fitting kit from Limora (supplier in Germany with very fast delivery). Part 213946. This turned out to be a Powertune RLE10117 (servo with fitting kit) which looks to be the same as the Barrett LE10117.
It came with air valve configuration as in your photo (cap with holes and sponge filter) but included an alternative cap with fittings as hose to use a remote air filter as is the original Mk2 configuration. This allows to keep the filter clean.
It was quite a fiddle to remove the old and install the new servo with the engine in the car. I did not need to modify the cowl but had to make a strap/bracket to support the servo on the valence surround. I used part of the fitting kit. I also replaced the non-return valve at the reservac tank and both rubber hoses. After difficulties bleeding the system (subject of my previous thread), I am now happy with braking performance and the blocking problem is solved.
Hope this helps you,
Dave

 

I removed the unit and its housing through the fender-well.

 

Me too. Some of the bolts holding the cowl may have required an angle grinder or hammer and chisel. While trying to fix the servo, I managed to take it out, partially dismantle, re-install it, bleed the system, and test the brakes at least three times in the same day before I understood what was wrong with it. It's one of those things that becomes much easier with practice. Of course, I was a lot younger then.

 

Finally reporting back. Had to clean up 3 years of junk and buy a lower profile jack.

I put the front end up on jack stands and can’t get the brakes to lock up even with aggressive pedal pressure and speed. I’m guessing the booster freed itself up with use. I’ll do a parking lot test before calling it good and continue to monitor.

Thanks, all!

 

Good news. So frequently servo/booster related. Hope it's solved. A servo rebuild might be in order or a Barratts exchange unit. They do a beautiful job. That's what I did.