Using a sealant might give you a temporary workround but its not ideal. Pain in the wotsit but it'd be much better if you can re seat it. That's going to mean getting the sheared retaining bolt out and finding a replacement
Other than that you're into replacing the section

Thanks for the swift reply! There are two bolts, one on each top and bottom corner (diagonally opposed only top left one is shown in the picture as the other is obscured by paint). They have both sheared and as the cast iron is original I would suggest that drilling them out would probably just destroy the aged screw thread shaft as the iron is > 60 years old.

I can get the cover off and file the protruding bolts to allow for the cover to make a coupled seal again and I was contemplating using EvoStik 'Sticks like Sh*t' (how did they get away with that name in the consumer advertising world ! ) as it claims to be unaffected by weather and temperature and can bond metal to metal in the wet.

I can't afford the complete replacement as that will no doubt be ~£200. What do you think? If I can get the access cover to marry up neatly and the bond works would that fly ?

I see what you mean about the old cast fitting being likely too fragile. I've never tried Sticks like **** and don't know how they got away with it. Does give you impression it should stick pretty well though
My concern would be that if you use adhesive to permanently bond the inspection plate you lose the rodding point if you ever need it.
Thinking more about it, is there any way of using some sort of external fastening system to hold the plate in place. What I was thinking was you sometimes see strap on boss connectors which hold themselves in place around the pipe with an external strap. If you could devise something like that with a new gasket round the opening to keep the seal, then you'd still be able to rod out if needed.

I think your advice is sound ( hence my use of the Forum !). Access later would be ideal.

I have spent about two hours internet surfing without any luck trying to find these bolts or even a replacement access cover.

Aybody any ideas on where I could source a cover or replacement bolts ?

Failing that Plan B is sealant and or metal cable tie fastening lashing of some sort.

if you havnt done it by know i would use some black silicone sealant round it and secure in place with a cable tie
let it go of for 24 hrs and then cut the tie of this should seal it

Asked and answered! Great forum and great advice....worked a treat!

Thanks

David
Scotland

Edinburgh wrote:

I also think so.

Wow..so useful posts for advice on sealing a pipe with sealants ?Thanks for the great review. I think I am going to add this one to my list of things to install this weekend.