I would suspect it's house marked. The MUR860 looks alot like your
description :

http://www.fairchildsemi.com/ds/RU%2FRURP860.pdf

Like they have the MUR and RURP, but there appears to be no difference
at all. Sometimes it's an insulated tab, providing it's metal, or may
indicate an all plastic case, but it doesn't say so here. The P really
does seem like it should mean plastic case but it is not on the
datasheet so I assume not.

Actually I have dispensed with dealing with most part numbers. You can
get half an idea what frequency it runs at, then the output filter on
that leg of the power supply can give you the approximate voltage.
Also, the value of the filter can allude to the approximate current
drain on the leg. Something pulling 3mA does not quite warrant an
8.600 uf......

All in all, if you're looking or a manufacturer out of curiousity that
is one thing, not that you'll find it. It's like Sharp taking an IC
and having it labelled RihX-4462-01ceZZ* when it is a friggin LM356.
Or Samsung with their KA numbers. (*that is not a real number, I just
made it up)

Reverse engineering is your friend. Look at the link real quick and
look at the circuit, most likely you have a replacement in an MUR, if
not I can find diodes that can replace almost ANYTHING in a TO220
case. Can't say zzactly what they might cost..........

J