Hello again Dr.

I wonder if you can tell me when Slingerland started putting gaskets behind their bass and tom lugs?

I have several 5-ply Slingy orphans from the early 80s with serial numbers in the 500,000s that both do and don't have them.

One set of toms (570,000 range) has thin plastic/rubber gaskets, while others (in the same serial range) have what looks to be roofing tar paper (I believe) that was machine punched - they are not home-made. And others still, from the same serial range, have none.

Any insights?

Thanks in advance.