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I bought mine in October last year and agree with Ramrod & Snoopy it's good advice, thankfully picked it up cheap enough ($1500 one owner) which made it worth spending the money on rebiuld and

allow a major service, I've been rebuilding it in stages, by nxt month the only thing that hasn't been rebuilt is engine and gearbox, motor is amazingly qiuet for 205,000klms (which are getting new main seal, full engine mounts & cam seals on distributor end nxt month).
Already done water pump, timing belt kit (genuine volvo), alternate and drive shafts, front and rear bearings.
Don't use the Stinger brand blue tooth for streaming and phone calls, not happy at all with it.

Also replaced boot struts as with the weight of the spoiler they'd worn out after 24yrs.
Can recommend Ash @DVS, their strut brace is self made and excellent quality.
Ash was very helpful with advice and ideas.
Check the condition of your steering rack, I rebuilt the lot, rod ends etc
I ended up going H&R springs with B6 struts and shocks, yes ditch the nivomats.
DBA grooved disc's, standard size as car is an auto and wife will be driving it, racing days are over.

Rebuild dash cluster next, there's a bloke on eBay in Sydney says he's qualified to redo VDO 850 clusters, anyone on here know who it is?
Usual odometer/speedo gears need doing to as well as bulbs.
Think the abs will get replaced soon to as TRACS light stuck on.
Then air con ready for summer.
These cars are 24yrs old now with 24yrs of wear and tear.
They need a good going over in order for them to last another 24yrs.
Enjoy your 850R Mazz, it's worth the effort, keep a log book of what you've spent and done to it.