Erratic time question

I have an Omega automatic Seamaster De Ville (without calendar) probably from 1966. It had sat in a drawer for 35 years. I had it serviced locally in late April.

Starting on May 30, I would occasionally check its accuracy. For the next 39 days it gained on average 1.86 seconds per day (spd), The next 26 days it gained on average 0.54 spd. The next seven days (by now it is August 11) it lost on average 1.71 spd. The daytime temperatures here were in the high 30's (Celsius) and low 40's. I don't wear my watch golfing and kept it in the car and we cool our house down to 27 degrees. I understand high temperatures will cause a mechanical watch to slow down so I wasn't particularly concerned.

Getting back to my records, the next 14 days, the watch lost on average 2.21 spd and the following 8 days (by now it is September 2, the watch lost on average 1.63 spd -- it had sped up. And the daytime temperatures were cooling off.

Then on September 4 I found the watch had lost two minutes in the past two days. On September 5 it gained one minute and on September 6 it lost one minute. And today, September 7, it hadn't lost or gained one second!

I took the watch into the shop today (the owner farms out watch repairs and servicing to a retired watchmaker) and he wasn't overly concerned and stated that it was an old watch and they can occasionally be erratic.

So, should I expect the watch to be erratic or is something going on that needs repair? That's my question. I couldn't find any postings that answered my question.

Any feedback will be greatly appreciated.

Thanks for the feedback. I am relying on auto-winding only. Every morning from now on, I will wind it.

As the mainspring winds down the force or power it delivers to the gear train will vary. Thai may be part of what you are observing. The way to do this would be to wind to full and then set the watch down and time it, perhaps over 8 or 12 hour intervals. That will tell you how it runs as it powers down.
If you wind it full everyday, I think you should see less variation in time accuracy. As long as your daily routine is the same. If you sit all morning one day and walk about the next, this will alter the power delivery over the day, and may affect the timing results.

Again, thanks for the feedback. All very helpful and appreciated. I just tried to wind it now (I have been wearing it for the last ten hours) and it won't wind. I am not sure just how much force is required to wind it and I guess I will find that out tomorrow morning. And I will conduct a twelve hour test tomorrow.

As I mentioned in my post I don't wear it golfing, doing outside chores, or anything near water. And next week, we're supposed to see a big drop in temperatures down to the low to mid 20's so temperature shouldn't really factor into it. Winter is on its way.