Advice on XML API integration project?

[Miklós]

Hi Pythonist software gurus out there,

Seems like I need to build some glue software between an XML based web
service and some third party client software/platform.
My planned man-in-the-middle has to exchange XML messages with a site which
has a well defined but baroquesc XML API, actually a set of XML messages
posted to that site and the response gets parsed.
The XML API however could change sometimes, there's versioning, etc.
I want the other end to have a rock solid constant API, I'm thinking
XML-RPC, so that the client side doesn't need to be changed or rather
that it wouldn't be complicated because of the need to do all that message
processing, API tracking, etc.
So the other aim of this glue layer is to dramatically simplify the client
side. (The client side is not in Python but some obscure language..)

The XML API has examples for all the message exchanges, so I thought this
could be used to track possible changes so that the code
of the man-in-the-middle preferably doesn't need to be changed, only it's
configuration.

Could you suggest software, libraries, contribute ideas, etc?

Thanks for any input in advance,
Miklós