Well, it's all apart and exactly as suspected there's a crack running along the leading edge of the link in the region between the larger diameter ends where the bushes are located. The crack was quite visible with the naked eye as stripped, especially with grease forced through it, but attempts to determine the precise ends of the crack using dye penetrant failed, possibly as a result of residual grease in the crack preventing the dye from penetrating. I cleaned the link with paraffin and then brake cleaner and an airline before a final soak in dye penetrant non-chlorinated cleaner so think I made every reasonable effort to get the grease out before putting the dye on, but as the pictures show, with the exception of one very slight hint the crack does not pick up. Applying a grease under light pressure however soon shows the extent of the crack, which must surely be the result of excessive pressure when using a grease gun. Looking at the failure and the load paths through the link I am convinced that it not a result of any suspension load and to be honest, I suspect if I hadn't noticed it it would be unlikely to result in a catastrophic failure, although, now I know it's there it's got to be fixed. The link is without question a mild steel forging (not a casting) and could be easily welded to a greater strength than the original part using a suitable argon arc process after pre-warming it in an oven, not-withstanding laws designed to protect us from ourselves. That said I could easily be persuaded to fit a good replacement if anyone has one going spare. I assume the replacement bushes will be supplied slightly undersize so they can be line reamed parallel to the rear pivot axis.
Thanks for all your thoughts, the bike was restored to a very high standard about 12 years ago (forgiving them this one aberration) and has been in dry storage right up until I bought it, so all the spindles/ fasteners etc are as new condition and free and easy to remove, in fact it's a real pleasure to work on.
