Roof leak - trying to find source

Hi folks,

Trying to find the source of a leak on my roof becoming more frustrating every day.

The house is an L shaped bungalow, cottage style, guessing 40s build, extention added around 2000.

So I have a leak on an inside corner, south facing,

https://youtube.com/shorts/E-_DL3Xeqvs?feature=share

It started as a stain on the wall, where the light switch is in the video.

I initially thought it was Condensation coming from the bathroom, but then I discovered there was water coming down the outside wall in the corner from behind thw facsia, I pulled off the gutter and to me it looked like the water was running off the roof tiles and wicking up underneath the end of the lead valley and down behind the gutter, onto the wall, and running down both thw outside and inside of thw wall.

I can't find any wet timbers in the attic, the only moisture I can find is If I pull back the attic insulation and get my hand down to the top of the concrete wall right down in the corner, which is where I was assuming the water was coming in behind the gutter.

I mixed a small bit of sand and cement and stuffed some under the end of the lead valley so that any water running off the tiles couldn't get behind the gutter, I thought problem solved.

About 3 days later we had heavy rain and I could see no water running down the outside so thought all was good. Unfortunately I started to notice water spots the living room wall, which is just inside the door where the water marks are at the start of the video.

I was trying to think back to when this started, and the only thing I could think of, was around the time the solar panels were installed back in February.

I called the installers and got them out to have a look, they could not see any issues with the panel install and pointed out to me that there was a crack about halfway up the lead valley.

So as a trial and error I put some bitumen roof sealer on it to see if it would stop the leak, unfortunately it didn't, as the water spots grew and new ones appeared.

I called a local roofer who lives nearby, he took a look and decided to try cutting the lead whee the crack is and put in a new sleeve of lead to cover it, he removed a number of the tiles to do it properly. the new section of lead goes about 6 inches under the upper section, and 6 inches over the lower section so the crack is well covered off.

He put some expanding foam under the tiles where he had to knock out the existing pointing, and repointed with fresh morter.

For a few days this seemed to be all good, we had some very heavy rain last Friday night and I couldn't see any water coming in, so was hopeful.

For the next few days all seemed good. Then we got some light rain and southerly wind one of the nights this week, and I could see a "snail trail" of water coming down along the door frame, where you see at the beginning of the video.

It's such a small amount of water coming in, which in a way is frustrating, if it was pouring in, it would be easier to find.

The roofer is away on holidays for a few days now so can't get him back for another week.

Anyone any ideas where else I should be looking, I am at a loss now.