Although I have upvc frames a couple of the glas units had failed, ive changed plenty before and watched pros fitting them so I just go online find a company to make up the sealed unit to my sizes and order them. You need to measure the size of your sealed units allowing for probably packing pieces between unit and wooden frame and work out the thickness of the unit as there are quite a few. I presume you have some sort of wooden beading around the frame holding the unit in. If the original sealing method was ok just refit the same. Hardest bit is working out the thickness of the unit but you can get calipers that will work it out for you or just measure framework and a bit of subtraction. This was the company I used last time and had free delivery as I was not in a hurry to replace. Double Glazed Units and Glass Sealed Units Online