I took a picture of the bolt-release lever on my Loewe Model 1893 Spanish Mauser. (It was built in 1894).
(The rifle underwent rebuilding, likely at Oviedo, but, still has matching original numbers on action, bolt, rear-sight and barrel. The replacement Spanish stock was numbered to match the original Loewe serial number. The original Royal Spanish crest is visible on the action-ring, but, faint).
The bolt-release lever is not numbered. It has the two styles of crosses shown on the OP's Boer Mauser.
I believe my bolt-release lever is an original Loewe part, but then again, it could be of Spanish manufacture. The cross on the spring is faint.
Attachment 114457