Might or might not need wiper motor assembly. Most can be revived with a little elbow grease and patience.
There's a GM Service Training Group (STG) textbook on wiper systems with some fairly serious troubleshooting and diagnosis guides in my manuals post below.
According to the table in the last few pages... The sections that apply to our CK trucks are;
- STANDARD ROUND MOTOR
- STANDARD NON-DEPRESSED PARK ROUND MOTOR
- NON-DEPRESSED PARK ROUND MOTOR PULSE
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8
RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.