As the title says, does the oil sump plug washer need to be replaced after every oil change, or can they be reused?
Background - my 2005 Daihatsu Copen needs an oil change every 3000 miles. I have always reused the washer in previous cars three times before replacing them, however these cars have far longer service intervals at 15,000 miles.
Personally I'm not seeing an issue with replacing the washer. This is a $.05 part. For my '08 Hyundai Azera, it comes with the filter I get from my Hyundai dealer. Does it really need replaced? Probably not, but the one time when it does need changed and you don't do it may be the difference between a $.05 part and a $2500 overhaul/engine replacement. To me it's just cheap insurance. Realistically, you probably would never see a complete engine failure due to oil loss, but you'd probably see a nice spot in the driveway, which can be quite annoying.
Replacing the washer depends on what the washer material is made out of. Most OEM parts are rubber based, so are both cheap and designed to be one use only.
There are also crush washers, which need to be replaced after every use.
There are a number of aftermarket (usually magnetic) sump plugs and washers - a large number of these have hard, flat, washers and can be reused a few times (< 10 times).
Servicing cars almost every day I would recommend replacing at least the sump plug washer every time you change the oil. I actually replace the sump plug as well where possible so the next person has a fresh head on the bolt to take off. Certain sump plugs have allen key heads which can become problematic over time.
The local company I get my parts from sells Corteco products. Corteco supply a plug and washer in a pack.
I don't have the exact details of your car but with a quick search on their online product catalogue I found one for the 0.7L model which may also apply to the 1.3L. The part no is: 220122S and it comes with a choice of two washers.
Flat washers can be replaced with the cheapo plastic 'squish' washers. They are not like metal crush washers but are thicker, soft plastic that 'squishes' into place when plug is tightened. They are only a few bucks for a bag of 100 at most parts stores, handy to keep in the garage and replace with every change, regardless of what the OEM washer was made of. All oil change shops use them, or are supposed to anyway. A few drips of oil on the ground at your home is just a spot clean, no big deal, but leaving a few drops in other people's driveways isn't always appreciated.
Both of my cars use flat metal washers (and neither one is something the local shops stock). Recommendation (manual) is to replace every time. I've never replaced either one (1991 and 1995 vehicles). Never a single drop of oil from either. If I did leak a few drops I wouldn't get too excited anyways since on the '95 the turbo oil return line has always dripped a little (replaced and resealed twice now to no effect, appears to just be a poor design).
However, my motorcycle (1994) has a crush washer and those are stocked along with the oil & filter, so it's easy to pick one up each time. Plus, even a drop of oil leaking in front of my rear tire is a crash risk I don't want to take. That said, I have reused a crush washer on it before. It's very hard to get the right oil level in the bike, air pockets for easily and it's easy to overfill, so I've had to take the filler plug out, drain a little, then stuff it back in (reusing the crush washer). No leaks as a result of that yet, so perhaps a crush washer can, in practice, actually be used a second or third time. Either way, I keep a sharp eye out for any leaks on that vehicle since it could be so disastrous.
