Mahle OC-91 is apparently the BMW OEM filter, sans logo.
Bosch 3330 and 72161 are the same filter, 3330 in mfg'd by Purolator in the US, under the Bosch brand. $3.50 a pop for either from rockauto
From the list at IBMWR.org, with a few annotations from me (wmax351).
Six oil filter manufacturers for K oil filter
Date: Tue, 8 Jun 1999 19:01:50 -0700
From: Roy Truelsen <email@example.com
As info, the pressure relief valve on the BMW oil filter is rated at 9-11 psi, same as the Fram 6063. The Fram 3614 is rated at 9-12 psi.
Other alternative filters for the K-bike include:
AC Delco PF-53
Hastings 157A, LF157
Motorcraft FL-271, FL-793
Purolator FCO-201, PER-241
Wix 51348, 51785
Sseven oil filter manufacturers for K100 spark plug and oil filter
Date: Sat, 7 Aug 1999 08:08:24 -0500
From: Jonathan Hutchins <firstname.lastname@example.org
Gathering together information to service my '85 K100, I found some details that didn't seem to be on the current parts list:
There was a lot of discussion on this ca '95-'96, with the engineering specs for the FRAM coming out as good or better than the BMW filter. Someone else pointed out that BMW does not manufacture their filters, but outsources.
Per Joe Senner:
• AMSOIL: ASF-57
• AC DELCO: PF-53
• FRAM: PH-3614, PH6063
• Hastings: 157A, LF157
• Motorcraft: FL-271, FL-793
• Purolator: FCO-201, PER-241
• Wix: 51348, 51785
Others including Rob Lentini have documented the Fram 3614, and I've used it; it's the only one I've tried.