As you are aware, the terms "firearm silencer" and "firearm
muffler" mean any device for silencing, muffling, or diminishing
the report of a portable firearm, including any combination of
parts, designed or redesigned, and intended for use in assembling
or fabricating a firearm silencer or firearm muffler, and any part
intended only for use in such assembly or fabrication.  Thus,
certain internal components, intended only for use in a silencer,
are silencers as defined.

If an individual made one of these parts, even for use as a
replacement part, the individual would be making a silencer.  Under
the provisions of the National Firearms Act, any person must apply
for and receive permission to make a silencer and pay the making
tax for each silencer made.  This would require the individual
owner to file an ATF Form 1 application for each silencer part to
be made with the payment of $200.00 for each application prior to
making any replacement part.

In regard to the two parts in your cited example, we consider a
baffle to be a silencer, but a wipe, which is usually nothing more
than a rubber or plastic disc with a hole in it, is generally not
considered to be a silencer.  Thus an individual owner could
replace a wipe.