first the not fitting stems. it seems there are more problems with stem fittings than i thought. the oven depth should be enough to house 26mm stems with a basket screen. i realized somewhen that the newer female joints were a bit less deep and started to account for that. there are a few units out there that can possibly have less room inside the heater.
solution: if you feel handy and diy, inspect the intake screen, if there is a bit room for the three glass tubes to move further back. if so, take a something wooden and a hammer and gently hammer each tube into the unit from the top by a millimeter and try the stem again. pay attention to not rip the intake screen in this process.
if youd rather not touch the heater, send it to me and ill adjust the tubes, or even place some shorter heater tubes inside if that is not enough.
@Shit Snacks please check yours again, i think i did put shorter ones in yours when it came home for the checkup.