Andy -
DRY CORK GASKET
Is the gasket rubber or cork? If cork gaskets dry out, then they will shrivel like a corn flake -- especially if they are out of the filter. Try cutting a new gasket (if is is cork). 1/8" Felpro cork-rubber gasket material.
WARPED LID
Set the glass bowl into the lid with no gasket, does the bowl rock on a high spot on the lid? Too much pressure on the bale can warp the pot-metal top. FYI - With a good gasket and flat lid, you only need to lightly tighten the bale until gas stops oozing from the top of the bowl. Tighten again in a few days if necessary.
If the lid is warped, then attach some 150g sandpaper to the lip of the glass bowl with double-stick tape. Insert the bowl into the lid and rotate it to buff off the high spot in the lid. The high spot will become shiney. Don't take off too much. It worked for my Durex 986640 glass bowl filter.
I don't recommend the following to flatten your lid, but may be necessary in extreme cases:
I put the lid in a woodworking vice with wooden jaws. I put a couple of pieces of wood under the area to bend. Then clamped with moderate pressure for a few days. Increased pressure and left it for a few more days. Did it help? I dunno, but at least it didn't break.
CRACKED BOWL
If the bowl is cracked, then check ebay. "Carter glass bowl filter", "Glass bowl filter", "Durex glass bowl filter".
DUREX FILTER
The Durex filter was produced by GM and was a dealer option. Durex Moraine #986128 (with thumb screw through the bottom of the bowl) was installed by the dealer 1947-1949. There are three different part numbers, probably because of different fittings that came with the original filter.
GM changed the filter to a bale and thumb screw in 1950. Part numbers were 986399 and 986640.
GM changed the filter to "AC" in 1956. It had AC on the lid. Part numbers 987500, 987629, 854345, 987500.
See:
http://chevy.oldcarmanualproject.com/1929_57chevyparts/57cmpc0319.htm- Lonnie