Metcal handpiece

e it

You don't. You bite the bullet and buy a new one. There's a new one on eBay for $77 or you can go to Mouser for $104.25.

I use my Metcal quite a bit and am still on the same handpiece for 15 years but I do have a shiny new handpiece "just in case". Also, my Metcal was bo ught used on eBay.

Actually I just managed to take it apart. I applied compressed air to the tip entrance and the guts popped out like a champagne cork.

So it looks as though the OP may as well carefully "Dremmel" into there and explore, and hopefully divulge if he finds weak spots, hollows , active areas etc

I'll have to remember that, for the next plastic superglue/welded box I come across

You open those by tapping them with the plastic handle of a screwdriver, working along the seam. A long time ago mikeselectricstuff showed how to do it on his youtube channel. I can't remember which video. The technique works very well.