Hello chaitanya,
Frankly speaken, I am not convinced either. The problem is that the purchase has not gone into stock as a service item, but gone directly to COGS from supplier invoice.
The manufacturing is some kind of a cake upon cake development during the years. We really need to redesign it to get it more professional. I hope that we can make some kind of developers talk regarding this.
I guess that most of it works, with some major changes.
Regarding the existing usage of service of bom will only work with additional overhead/labour cost entry.
However, you could also solve it by letting the service item be a purchasable item. Instead of using the existing stock gl (inventory) account you could use another account in the GL for this. You could do me a favor testing how this would work.
Best regards
/Joe