Well there was nothing for it really but a complete restoration. My thoughts were that since I had already been deprived of my preferred option of carrying out a sympathetic restoration, I would instead restore the set to be as reliable as possible.
I needed to get rid of that black paint and I could only do that properly by completely stripping the chassis. All the wiring needed replacing too - it was just dangerous.
I spent quite a while carefully dismantling and stripping down the metalwork. Once I had a bare chassis, I removed the black paint quite easily with a jelly-type paint stripper applied to small areas at a time.
The chassis was quite discoloured underneath due to light rusting in places and was the original reason for the black paint being applied I assume. I repainted with Smoothrite - silver for most of the metalwork and black on the underside as per the original finish.
As for replacement capacitors - I would have liked to have restuffed the original wax components with modern versions if they were in a good enough condition to do so. But as they had already been removed and were no longer an option, I replaced with 630V rated yellow polypropylene types instead.
I decided I may as well change all the resistors as well, since several needed changing anyway or had been caught with paint. I replaced with modern 2W metal film types because of their similar dimensions to the originals. The two can-type electrolytics were both restuffed with modern components and refitted at this time also.
At least the set now had a consistent type of capacitor and resistor fitted of the correct values and in my opinion looked much better for it even if a little more of the remaining originality had been lost by doing so.
I eventually got to the bottom of the long wave problem when I noticed in both the antenna and oscillator coil cores for that band, what I had originally took to be just sealing wax, was actually Araldite as well.
After careful removal of the glue I discovered the two original slugs were missing and broken pieces of ferrite rod substituted in their place. I can only surmise the original slugs were knocked out and lost in the delivery accident that damaged the case.
Fortunately I had several of the correct type of slug to hand, fitted two, realigned the band, and was rewarded with excellent reception.