Provided its a dry lube then it'll be fine and probably a good idea- years ago when I couldnt afford gear I used to spray inside of boom and they lasted me years. Now i'm more likely to snap them from going past the limit than them breaking from corrosion.

The white stuff is best if you can get it, failing that just the pressure pack silicon dry lube.

You would also be better off just spraying the 1st six inches of boom arm and inside the tubes, otherwise if you grab the extension in duck gybe or whatever it'll be a bit slippery.

McLube Sailkoat/ Sailcote is good stuff.
From any boat chandlery.
Dry lubricant and works great on boom arms etc.

Quote From Roger Jackson of Starboard Fame.

"As far as keeping your new (older) boom working well, get a hot water hose, remove the tail piece from the head and boom tubes, then rinse out the inside of the boom tubes thoroughly, rinse off the extension tubes, and rub a bar of soap over the extension tubes while they are still wet. Rub some soap on your finger and put some soap down inside the boom tubes.
When you slide it back together I think you will like the smooth way the boom slides for adjustment."

lubricants are for sex and engines.

windsurfing parts should be disassembled, rubbed and flushed with fresh and allowed to dry.

soap may help epecially under your armpits.

end of story.