To see which current offering is best I purchased 4 brands listed for a 73 350 on Rockauto. These are supposed to be rubber replacements for the OE rope seal. First off is National. The OD is too large to fit into the timing cover. Not sure what application it would actually fit. Made in Vietnam Next is Timken. Same dimensions as the National seal. Also does not fit. Made in Taiwan. Next is Fel Pro. PN 15200. Will fit the timing cover. Is rubber on the OD. Package says made in USA. Mexico is molded into the seal??? Last is Mahle. 65025SF. This is a metal OD seal that may need a little sealant. It came with a very detailed instruction sheet. Made in Taiwan. All of these are meant to be installed from the inside of the cover. The first 2 may be for newer style covers that install from the front but I didn't have one handy to check. I have not installed the Mahle yet but have used the Fel Pro in the past with good results. Pricing is similar for all 4 at around $5.