Does oil degrade over time, useage or both?
I’ve looked at a low mileage Sports Tech (60 plate, 35k miles) and the owner says he services it on mileage not time. Whilst it’s had an engine oil change every 2 years, it’s never had the gearbox or diff oils changed. What are the issues with this? Obviously, this would be one of the first things to sort, but could their be any problems with this?
TVM! 
Don’t get hung up on how long oil lasts, how often should I change it etc. He sounds very sensible changing it when it’s due on mileage. Each will have there own ways of servicing a car, full dealer services each year, great irrespective of mileage.
Mine has that up to 8 years old, then it’s been done by myself and generally had an oil change each year at around 5k miles, that’s all I ever do annually.
This last year I’ve missed the oil change on both cars as I’ve barely done 5k miles in the two, I doubt they’ll suffer for it.
What I am a stickler for are brakes, both have had a full strip down service. Also attended to anything else that needs it, especially cleaning and any rust treatment, a must.
Others will have their take on this I’m sure. Most of all a well maintained car with the oils checked and changed when needed is the thing to watch out for.
And additionally, yes I’d be changing the gear and diff oils as soon as possible, seems like it’s needed on that car as a starter, well I would if buying.
As long as there is evidence of good quality oil being used, it looks like it’s been changed every 2 years at approx 6k miles, modern synthetic oil easily stays effective that long.
Just a shame the gearbox oil wasn’t done, believe it’s at 5 years in the schedule.
I would not be over-concerned about the gearbox and diff oils not having been changed in 35K miles.
But I would change them or get them changed if they had been in for a number of years and a 60 plate is now getting on. At least you will know they have been changed and it’s a relatively small cost.
I’ll echo the above - synthetic oils easy last 2years. If you buy it, change the oil all round.
There is more, much more, to servicing than an oil change.
How often has the brake fluid been changed?
Has the gearbox and diff been checked / changed?
Have the filters been checked and cleaned…rodents like to nest in unexpected places…
Has the coolant been changed - it may not be due, I can’t recall.
If oil is only being changed every 2-3 years, what else is not being checked?
Agreed, if you are not sure any of the fluids have been changed then do it anyway, none of them are expensive and you could do all the jobs over a couple of weekends. In addition while you are bleeding the brakes check the slider pins and re lubricate them with the correct lubricant plus check the caliper pistons and pads and put some rubber grease around the piston seals.
I agree, if no record of service change the important stuff.
I’ve just changed my diff oil, I drained perfectly clean (looked new) oil out and put new back in.
I didn’t know, it does say on my service history the gear oil had been done though.
Mine only does at most 3k a year, I change engine and diff annually and gearbox every 2 years.