gt, from the sounds of things it's a shooter grade collectible, if there is such a thing.
OP the problem you mention is not uncommon.
When I was in South America back in the seventies, a few of the nations I visited were still issueing M89/91 type rifles to their police. Many of them were gorgeous carbine versions chambered for the 7.65x53 cartridge, which was so popular in Europe at the time of manufacture.
Most of the rifles I saw were in Peru and Argentina and most were in surprisingly good condition. Bolivia would be a runner up for the amount still in service.
The condition you describe is not unusual for these old rifles which were often stored in hot, dry locations and not properly serviced for years.
One of the main reasons a lot of those rifles were in such great condition was a lack of ammunition and of course the police officers wanting to use the more modern firearms in their racks. Sadly this situation led to lack of stock serviceing, such as a coat or two of Linseed oil every year and as this sort of upkeep was left up to the local police detachments, it was often neglected.
What I did notice, in Argentina was a police armorer that had a bit of a love affair with the M89 and M91 variant rifles that was actually trying to save the few he had control of from deteriorating.
He added thin wooden strips under the trigger guard by shaping them by hand and glueing them into bottom of the inlet around the trigger/tang and king screw area.
He then cleaned and added Linseed oil to the receiver and barrel inletting about once a week for a few months, then wiped off the excess and reassembled the rifles with their matching components if possible.
The key to the Linseed Oil wipe downs was to let it DRY properly between coats. He mixed the Linseed Oil with acetone or alcohol so that it would penetrate deeper and dry faster.
These old rifles need to be properly maintained, especially if they're going to be shot. It's far to expensive to take it to a smith, if you can find one that knows how to do it properly or is willing to take on such a job that takes up a lot of time for very little if any return.
This means you have to do some due diligence and do the job yourself or take guntech's good advice and make it a safe queen.