Twincast and Soundblaster

mib unused Twincast, c-9.5

The first Blaster toy was redecoed as Twincast in 1987 and had its tape-door retooled in order to accommodate two cassettes at once. The clear-plastic part of the door was also changed to clear-red, so when certain cassettes were placed inside, the "secret plans" decals on them would reveal the "weak point" of either Fortress Maximus or Scorponok, much like using the tech-specs decoders. He came with Steeljaw, who was given one of these new decals.
In 2006, Twincast was also reissued as an e-Hobby exclusive, this time packaged with the new character Flip Sides.

mib unused Soundblaster, c8.5

As part of the Japanese Headmasters series, Soundwave was redecoed and retooled in 1987 so that he could hold two Cassettes in his chest at once. Soundblaster's tape door was cast in transparent red plastic to allow the information on the "readout" decal, unique to the Headmasters decos of the cassettes, to be seen, functioning in the same manner as the Tech Specs decoders. The readouts of the Decepticon cassettes showed the "weak points" of Fortress Maximus. Soundblaster came packaged with Buzzsaw.
Soundblaster was also reissued in the Transformers Collection series in 2005, packaged together with Buzzsaw and Ravage. This mold was used for all future reissues of Soundwave, since the original Soundwave mold is broken, and they mostly just have a single tape door to let it look more like Soundwave, yet they still feature the more exposed buttons on the bottom of Soundwave's chest door.