Well, with 88k miles it will still be solid, but taking it to a BMW garage for a service won't give you that much return when the day comes to sell... so I'd suggest you find a local independent that specialises in sports cars AND who knows BMW's.
If you're anywhere near the bizzy lizzy bridge in Kent am happy to recommend an independent who's looked after a couple of my past motors, as he used to first race his M3 then after it got sold on, ended up looking after it even when it was being sponsored by the Red Bull team. It's a backstreet workshop, not some posh premises but a quick view of the metal normally parked outside should give you an indication he knows what he's doing.
Don't forget yr pickies & add them to the 'us & our Zed thread'
J