Unfortunately the flow indicator cracked as well sometime after I used plumber's tape (within a 3 year period). I couldn't source a replacement for it online at that time so the 2028 went in the trash.I replaced my 2028 Primer button O-ring, although Eheim refuses to sell them. But that big O-ring is indeed available elsewhere and replacement was rather easy.
Available where, you ask? Let me quote from this link found in Cichlid Forum
The sizes you will need are 4.5mm X 92mm for the motor/primer and a 2.5mm X 12mm for the flow control indicator.
This is what I ordered:
N4.50X092 Metric Buna-N 70 O-ring$2.80
2.5mm X 12mm Metric Buna-N 70 O-ring$0.22