I hope, you have now successfully treated the leaking area.
Finding the actual source of leakage is becomes a very difficult task due to covering of hole area.
The treatment which can be done
1. Pressure grouting at leakage area from negative side (from where this leak is seen) - this may not be a 100% proof solution because you just sealed the one leak and not the source of it so there may be possibility of leakage might coming at other places.
2. Reworking the hole area - it involves huge cost.
3. Identifying the source of water and doing positive waterproofing at it to completely seal the entrance - this involves thermal imaging technique which is used when we are not able to identify the source. with the help of thermal imaging technique, the agency do capture the thermal photographs of the structure where, we can trace the route of water coming down.
4. If the leakage is happening through the gutter area only, try to find the damaged cracked areas of waterproofing in gutter areas and do rectify that with cement mortar. If the waterproofing is damaged at many places (better to apply a coat of waterproofing plaster on it). if you are not able to identify source but you are sure about it is happening from bottom of the gutter and not from the top portion of beam, you can prepare a cement slurry which is more like a watery and pour it into the gutter by plugging the drain for say an hour. that cement slurry will run through the cavity from where water was seeping and particles of cement will get stuck / locked into it which will further form a bond with crack and will bridge it completely.
5. If its difficult to identify and is not getting stopped, the another method which you might consider after taking quotes for renovation of same. covering the whole roof area with GI sheet roof (same like how we see roofs on many building in Mumbai Areas).