The Repair Pack item does not convert to a fluid when extracted. This occurs both when attempting to pull from a chest or an assembly machine (although I only tested with tier 1).

Really enjoy the mod though, great work!

To add to this neither locomotives nor fluid wagons can be liquidized

Ah yes - just saw DocJade's video.
Fixed for 1.1.5 (along with decreasing the buffer size in liquefiers though solidifiers still store a full stack of a given item - factorio limitation...)

Would it be at all possible to reduce the stack size of the output, similar to how assemblers can increase the stack size in their input?

Unfortunately not - due to the input being a fluid (and nothing else) it will 'force' the assembler to keep producing until max stack size as opposed to based around assembler limits.

Didn't want to make another thread for this, but it seems like rocket launchers are not liquefying either, which makes it a bit hard to automate Spidertrons. Thank you for getting the last couple of those by the way