We have a small piece of eavestrough in our shop to show the incorrect way to fix leaky corners. Its not that they can not be fixed, but the old caulking should be removed before a new layer is installed.
No matter what product is used to try to seal a corner, the surface should be as clean and dry as possible. Sometimes the old sealant will pull right off and other times its super tough and may need to be slightly heated with a small torch and then scraped out.
A eavestrough that is this old and worked on so many times is pretty much a lost cause and should be replaced.
We are happy to provide a free quote for your new eavestrough system. We are primarily working in the Scarborough and North York regions at this time due to high demand and winter closing in.
North Shore Eavestroughing. www.eavestrough.ca 416 615 0443