I do not know when you bought the Feuling Lifters you had problems with, however a few years ago (old style lifters) had problems. Feuling quit making them and introduced the newer styel.
Some one got a hold of the old series and people like Smok and Flames were selling them on Ebay, and some had nothing but problems with the.
I know this as I was one of the many who did purchase from Smoke and Flames, I found out about the problem on the HTT (Harley Tech Talk) website as others were having the same problems as you mentioned. Luckily I had not installed them yet.
I got a hold of Feuling, they confirmed that Smoke and Flames were not an authorized distributor and somehow got a bunch of the discontinued lifters and were selling on Ebay. They requested I send the faulty lifters to them (Feuling), which I did and they sent me N/C a new set, I never did have any problems with the Feuling Lifters and feuling Oil Pump in my 95" build c/w SE Heads and SE 251 Cams.
Talk about customer service.
I hope they get the problems of the death of the founder out of the way and get back to building and selling parts,