I don't actually believe this.....so I've been messing on with this since 8am this morning. Finally manage to get into the USB boot stick using Ext2Mgr...and guess what - there's no vendor file!!!!! Just boot / rd / zimage files!!!
Rinning DS3612xs_3202-Repack.pat / microserver-dsm-4.2-02.05.2013
ARGH!!!!! I could actually start crying
Edit your grub.conf file that's on the usb stick and add
#vender /vender show
#hw_model
kernel /zImage root=/dev/md0 ihd_num=0 netif_num=4 syno_hw_version=DS3612xs mac1=your macaddy mac2=XXXXXXXX sn=B3J4N00xxx
And add 3 numbers were the Xs are. Reboot and see.