I had since 1999,3 Ongaku,Gakuon,Neiro,Neiro Silver,2 Souga,Baransu,M7 and M10.
Also my 2 friends have old Ongaku and i and my friend never had one problem with them,so you can buy without any problem,you have to check only the tube.
I also did comparison in my home with old Ongaku and new Ongaku KSL,and new KSL is better because is more open,natural and more clean sound,but if you can buy an old Ongaku will be you happy for all the life