[Lingtyp] grammaticalization ABL->?

[Ludwig Paul]

Dear colleagues,
I am working on the grammaticalization of Old Persian radi "because of" 
through Middle Persian ray "for (the sake of)" to the New Persian 
indirect and (later) direct object marker -ra (all three follow the noun 
they govern). This grammaticalization process was discussed by Bossong 
1985, to whose inspiring study other scholars have referred since then 
(e.g., Hopper/Traugott 1993, p. 158). (the account given of this 
grammaticalization process is not very accurate in both these works, by 
the way)
My focus is on the development of Old Iranian *radi in modern West 
Iranian languages other than Persian, where postpositions or case 
markers with the following functions have been derived from *radi:
a. ablative/source
b. general oblique case
c. benefactive, later indirect, later direct object marker (like in 
Persian), or instrumental

The development of case c. is well-documented through Persian. To 
explain a. and b., I looked - unsuccessfully so far - for 
parallel/similar cases in other languages where a postposition meaning 
"because of, on account of" (cf. German "wegen") has become a more 
widely-used (grammaticalized) postposition, or case marker.
Does anyone know about such a development in any other language or 
language group? I guess this is not very frequent typologically, and 
would be grateful for any information. This may concern a similar 
diachronic development, or a synchronic variation in closely-related 
languages that allows a diachronic interpretation. There is no 
information given on this issue in Heine/Kuteva 2002.

Bossong, Georg. Empirische Universalienforschung. Differentielle 
Objektmarkierung in den neuiranischen Sprachen. Tübingen 1985.
Heine, Bernd and Tania Kuteva. World lexicon of grammaticalization. 
Cambridge 2002.
Hopper, Paul J. and Elisabeth Closs Traugott. Grammaticalization. 
Cambridge 1993.