I'd say it's a high price too. My late '91 300E with 192k on it was $5200, and I think I over-paid slightly, though the condition inside and out is very good and it has almost every option- leather, sunroof, dual airbags, asr etc.
Other TE owners will have advice but with this many miles you need the service history. There's also the rear suspension which I believe can be a pain on these wagons and an expensive fix if not working properly.
For an '88 with that many miles I'd agree with the other poster on price.

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1993 320TE M104
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past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
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"music and women I cannot but give way to, whatever my business" -Pepys