I have just found this forum a few minutes ago. In the seventies I had a HP-70 during my aprenticeship here in Switzerland. Now I have returned to buy a 35s, but it isn't the same, the vintage models were of some true quality. So if you would like so I would be glad to repair your hardware in question. Here in Switzerland a big HP fan, Juergen Keller, could give me a help also, so your machine for sure would be in good hands.
Best regards to you and all the best.
Christian Berner, Rupperswil, Switzerland