1999 boxster 5 speed manual transmission issue

[jdlmodelt]

So, the past two days in cold weather, my 5 speed was not smooth like it has been in the past. It felt resistive mechanically, not like you would expect from cold weather, thick oil. I replaced the transmission oil and discovered metallic color in the oil and also 3 or 4 1/16 size metal pieces in the oil. It just resits a bit when cold, does better when warm, and makes a subtle, VERY subtle howling sound in 4th and 5th gear. Mostly in 4th gear. Still hear it with the new oil change. 1999 Boxster with 124k miles. 5 speed manual. I"m wondering, do I pull it and hope to fix it or pull it and replace with a used warranted tranny?