think this bit is quite important for you
How to make backup of stock recovery
download dump-recovery-signed.zip and put it as update.zip on root of SD card (e.g. /sdcard/update.zip) *1 *2
install update.zip from stock recovery *3
stock recovery will be dumped as dumped_recovery.img and /proc/mtd will be copied as dumped_proc_mtd.txt on root of SD card. keep them in safe place.
read this thread as there is some advice on here viewtopic.php?f=15&t=1390