Well the one that is for sale in my area is the gasoline engine variant.The 1983 had the HT4100 (4.1 liter) engine. It is terribly under powered.
The diesel was no better.
Here is a clip from Wikipedia.
"In 1982, Seville offered heated outside rear-view mirrors with an optional rear defogger. Inside, a "Symphony Sound" stereo cassette tape system was available. The previously standard diesel engine became an option with the introduction of a new 4.1 L (250 cu in) HT-4100. This engine had a number of reliability issues, such as weak, porous aluminum block castings and failure-prone intake manifold gaskets. "
Head gaskets where also a problem.
If I there was a Riviera or a Toronado for sale in my area I would go for it but currently there is a only an early 80's Seville and Eldorado.Based on the responses above and more on Cady's engines of that model, I'd offer one of the wisest decisions would be NOT to consider any Eldorado/Seville from that gen. On the other hand the OP would do well to keep an open mind with the '79-'85 E-body Buick or Toronado. The 403 in a friend's '79 Toro performed well, and I really enjoyed the Rocket 350 Olds in my '80 Riv. I had 2 other Rivieras with the 307 Olds offered later and both ran pretty well considering the pitiful smog HP numbers back then. Mid ''80's offered a Riviera T-Type with a turbo V-6, but no memory of its performance. Just some things for our comrade overseas to consider if the lines and drivetrain are other wise attractive and not set on a Cady.
I am in Lithuania, appearance wise of the car I am in favour of the unique rear end as it makes the vehicle look very quaint in my opinion, if I find a Riviera or a Toronado I'll go for that in a heart beat but so far there's no luck.Anytime I've read a similar question the consensus is the question isn't whether or not the HT4100 will go bad it's when...meaning they will all go prior to what most people consider as normal. In addition it seems to be a fact that the HT4100 is less rebuildable.
That said if you buy it with the idea that you will need to change the engine when it goes bad and you adjust the price accordingly it would be possible to install an Olds small block in the Seville. All of the parts needed existed in the Toronado and the Riviera (1979-1985). You will need an entire set of brackets. They do not necessarily need to be from an E-Body Riviera or Toronado but having a Riviera or Toronado would make it easier.
I personally cannot stand the look of the "bustle back" Seville. I think the Toronado/ Eldorado and Riviera are much better looking cars. The Toronado and Riviera will have much more reliable engines once the Seville/Eldorado moved to the HT4100. If you find an E-Body in great shape please do not sacrifice it to save the Seville. Any set of Oldsmobile brackets with the AC compressor on the passenger side, alternator on the driver side should work. The fan shroud is a question. You will need to get engine mounts, should be replaced anyway, and you will need to at least rework the AC suction/discharge hose assembly. None of that should be that challenging. The radiator shroud might be a question but without trying it I wouldn't guess. The left/right position should be correct but not certain about the up/down location and not certain about the distance from the radiator. There's also an axle support bearing/bracket which may be specific. I'm not certain how close the similar bracket is for the HT4100.
Where in Eastern Europe are you?
Well one of my relatives there swapped a Volkswagen Passat B3 engine for a Seat engine so I do not believe there should be any issues regarding swapping engines.I don't know about Lithuania specifically, but in most (all?) of European countries, doing engine swaps are either outlawed or an administrative nightmare. The "grey card", equivalent of the car title, lists most of the characteristics as weight, HP, displacement, number of seats, outside colour, etc.
Changing one of these characteristics leads to having the title changed and an inspection will be conducted, you'll have to show homologation certificates for everything that is not stock. And you can't hide it because you have mandatory safety inspections at regular intervals.
I put better brakes (the PowerStop kit with bling-bling drilled/slotted rotors, yeah I know) on the Seville. Nope, no way. Had to buy plain rotors in emergency to pass as the maker did not have a certification sheet that certifies these are conform and made for a 1992 Seville.
So yeah, if OP bites the bullet, he may have to stick to the HT4100.
Any old Caddie is a wise choice for driving for the pure pleasure of driving a classic. However, there will be constant challenges driving and parking. I say go for it.I am keen on getting a luxury malaise era American car as my first car and I found a decent condition 83' Seville for sale, I would like to also say that I do not live within the U.S. but in eastern Europe so I assume parts maybe a difficulty.
Wise choice for owning*Any old Caddie is a wise choice for driving for the pure pleasure of driving a classic. However, there will be constant challenges driving and parking. I say go for it.
Robroy,the Swedish market is not that far away for you, below a few cars from that era for sale now, divide with 10 to get to €