What is the procedure/steps to be followed for preserving a Gearbox with Antifriction bearing and Force fed lubricated. This spare Gearbox has been recently overhauled and we need to store for long time( say next 8-10 years)
One recommendation is to fill to some level with anticorrosion oil.
what is the best practice of storage.

"Machinery Lubrication" magazine has published articles in the past on storage of equipment you might check the archives. Storage of equipment ideally is not a hide it and forget it excercize.

Even stored equipment requires frequent maintenance if you want to keep it useable. Minimum maintenance should include; turning shafts on a regular schedule, checking for and preventing internal corrosion, and maintaining lubricant in good condition, store it under climate controlled conditions, protect input and output shafts from corrosion with a coating of grease or cosmolene and wrap with protective fabric, paper or tape.

To reduce corrosion on the internal componants you could fill the casing with lubricant leaving just enough head space to allow for temperature expansion this will put all rotating components under the oil level and should minimize or eliminate any surface corrosion of the gears and bearings. Monthly turning of the input shaft several rotations will move the bearing elements to reduce false brinnelling, will A Vapor Space Inhibitor (VSI) additive should help minimize corrosion on the surfaces not covered by the oil.

Use Cortec VCI 369 N concentrated neat oil and spray evenly inside the gear box and use VCI 329 oil after calculating the volume of the gearbox. Make sure all the vents and opening on the gear box are tightly sealed. VCI based product will give a long term protection in Liquid, Vapor phase. What is the peiod of protection you are looking for?