Comman invoice for Excise and Service Tax

There can be common invoices, there is no problem in this regard.

The complexity of business/transaction is increasing. The accounting system must be able to capture this complexity; so that as and when any query arises from any of numerous government agnecies, it can replied satisfactorily.

gross job is restoration of damaged machine ....................

scenerio 1 ............. use seperate bills for spare parts , charge excise / vat, seperate bill for maintanance and charge service tax.

scenerio 2 ............ as mentioned by you, direct transfer of inputs to end user and processing + maintance to be billed and service tax charged.

if u opt for scenerio 2 then get ready for scenerio 3 also 

scenerio 3 ........... audit party consider the damaged machine as input and ask u to pay full excise duty  of new machine value ..................... as reconditioning of damaged machine amounts to manufacture !!

seperation of accounts from one to another department always prevents unwanted litigations.