I have put filters in those locations after having a tank cleaned and sealed. So, nothing to be alarmed about, IMO.

I used a white sealer (now prefer red) on my 41 tank many years ago. Like Martin said, if it's the original tank, that's probably what it is.

I don't like messing around with cleaning and sealing tanks any more. If you can get a replacement (and I think you can), I think it will save you time and $ in the long run.

~ Victor
1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery
1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~ moved on to fellow Bolter