The result of inspection by a professional was that there are only 2 way to repair, one is a repair by sealing between the glass and sash, another is to replace complete top light window assembly with new one because the window was already discontinued production so only sash (without base) cannot be replaced with new. The cost for sealing is not cheap, moreover, the cost for scaffold is much more expensive than repair cost. Therefore, I decided to re-paint roof tiles together to save scaffold fee for next time of roof maintenance.
The original color of the roof tiles were dark green, but I selected dark chocolate brawn this time to coordinate the color with main house and main garden which are typical Japanese.
There is no concern of rainproof of the roof for about 10 years after this time of maintenance, but I have spent unexpected huge cost for the maintenance.