Your vendor is joking or what ??
If resetting the MSC improves the QoS in the network for few days, there is only one solution :
CHANGE THE MSC !!
But before that :
Can you be a little more specific about the TCH drop cause ? The QoS indicator “TCH drop” should have some sub-indicators, such as “TCH drop due to …”, “TCH drop due to …” and so on.
Does the TCH drop increased on ALL the cells in the MSC, or just some random cells ? By finding the shared equipment (board, interface link, …) between those cells, you might detect exactly where is the faulty HW.