FWIW, Marlin individually fits every rifle's BP & PG cap, including the spacers.
When the spacers yellow, a touch of emory cloth turns them white again.
When spacers shrink from age, or go missing - "used" replacements may/may not fit YOUR rifle's stock, as in: "too small".
"New" spacers are supplied oversize & must be fitted, as in: the outer edge sanded even with the stock.
Since new spacers usually need to be fitted anyway, white line spacers are easily made from empty/cleaned white plastic household bleach bottles.
Just cut an oversize piece from the side, and attach it in place (held by the buttplate & screws).
The excess white plastic is easily pared down to wood level with a small/sharp carving/pen knife blade.
.
