Not sure if a bug or intended (okay, almost sure not intended but still better check here first).
Steel into aluminum is rather amateur alchemy as far as CDDA goes.
You can make a muffler from normal steel, and then disassemble it into a bit of platinum.
http://cdda-trunk.chezzo.com/muffler
Philosophers Stone, in my muffler?!
It’s more likely than you think!
Materials: Steel
I don’t see any platinum there…
Look under disassemble:
http://cdda-trunk.chezzo.com/muffler/disassemble
Somebody has confused mufflers with catalytic converters.
To be fair, since there are no converters in the game at the moment, they just slapped converter’s “functionality” onto the closest part that does exist.
“functionality” in this case being “to serve as a source of platinum for actual catalytic converter used for chemistry”.
Heck, what about those platinum dental grills all the little kids are wearing? You could build a platinum golem out of the various jewelry bits and bobs one finds on zombies. Who needs to get it out of mufflers/cats?
Besides, it’s not like your average survivor can extract the platinum from a catalytic converter. It’s not like there’s a chunk of pure platinum in there. It’s spread out along with palladium, rhodium (and maybe others) in a washcoat (often aluminum oxide) over a substrate, typically a ceramic grid. It’s recyclable, but requires an industrial process to do it.
Ok, so it’d be a small platinum golem. But why not, since most of the jewelry seems to be found on small zombies? 
Well, I’d say it’s the same for getting solder back by desoldering/disassembling PCBs. I mean, it’s totally possible, just not very easy to do - on a survivor scale.
Especially to reuse it without any flux might be a problem…
I guess the antenna and muffler conversion to other materials is not seen as a big problem, since the gain is very little (as in; why bother to get alumin(i)um that way while it’s plentiful on solar cars and some other sources. Same for platinum (and it doesn’t have much use anyway)). I guess that’s also the reason why nobody took the time to fix it yet.
Also, I consider it as a “fair payback” for having, for example, the steel broadsword in your hand completely disintegrate into thin air if you don’t fix it in time.
Not everyone is playing with vanilla item spawn rates.
I always play with 0.01, for one.
Under these circumstances it’s actually important to know where you can get resources reliably.
Since most of the time this platinum is going to be used in a catalytic converter for chemistry anyway, I don’t even see why you would try and disassemble this unit in the first place — instead of just using it “as is”.
screams in possum
I Love you.