I loved the cartage PF141 filter $1.99 at pep boys never had an issue with the o ring, I would only change oring every 3rd oil change.
GM also used the designation "M-40" on the options list and some ID tags on TH400's also...the TH350's were "M-38" for the plain 3 speed ones, the lock up converter ones were labeled an"MV4"..I have never heard of the th400 being called a 3L80. Learn something new every day.
Oops, I think I’m wrong. I think it’s the heat shield that is mounted to the bottom of the intake manifold to keep from coking the engine oil( doesn’t work)#7 is the heat shield for the rams horn exhaust manifold. Got one on my 68