Hello all, brand new to the community. Approximately 1 month ago I purchased my first plane, a 1957 V-tail Bonanza H-35. Plane has 20 gal mains, 10 gal aux, and 20 gal tips. She's always been hangared but the owner got sick and stopped flying so she's been sitting for about 15 years with full tanks (except tips). I bought it with a fresh completed annual and inspection passed. Anyway, I've taken her up 5 times both with my instructor and without. Each outing, we have switched to the aux tanks. Every time we switch, there's no fuel pressure and engine dies. When switching back to mains, the engine comes back to life. Once the switch was made to aux, we only gave them about 10-15 seconds to feed to the engine in the hopes that it would start, except this last time. I was solo on a 1.5 hour flight cruising @ 8,500. Decided to try aux again knowing that it would fail, but with the intent of giving it more time to try feeding the engine. I figured that since it had been sitting for so long, there could be air in the lines that would need purging. I made the switch to aux and as predicted there was no fuel pressure and the engine died. I tried using the electric fuel pump, nothing, I tried using the wobble pump (yes it's still installed), nothing. I waited for an ETERNAL 45 seconds before switching back to mains. Engine didn't start right up, but once I used the wobble pump to get a little pressure, all was good again.
Aux tanks are full, they sump fine, and there are no leaks that I can tell. Is there something that I'm missing? What could be the issue? Thank you in advance for your support.