Altissimo Register Issues

[iClarinet]

I've been playing clarinet for about 7 years now, but lately the third register E natural and up haven't been coming out unless I honk really loudly. When it does come out, it isn't steady at all and squeaks a LOT. I have an overhauled Penzel Muller from the 1920s and there are some cracks in the wood...I know I need a new clarinet but I just don't have the money for one (broke college student ya know). Until I can get a new one, does anyone have any tips for making these notes "prettier"? Thank you so much