Does Lean concept helps Job shop unit without its own product & 100% depends on his customer orders which fluctuates to the tune of 30-40%

Yes Lean management is spirit and idea, not just simple system of specific tool where offered by most of consultants. Lean will guide you like a map, but you are the one who should create your own work system, to reach your target. Of course you can use and you should use kaizen, TPM tools as basic, but how and when to use depends of you and your staff. You will never achieve your % goal if your staff from each and separate job unit will not feel are the part of Lean creators. Than you can everything. faster, better and with big savings where from other side increase customer level satisfaction.