Welcome to the site!!
First off, it sounds like your rear caliper will need to be rebuilt or replaced.
The piston is sticking in the bore causing the brake drag you mentioned.
If the caliper piston bore is too badly corroded, it will probably be best to replace the rear caliper. If the bore isn't too badly corroded, then rebuilding the caliper may suffice.
If the rear is that bad, you may need to closely check the fronts as well.
If the brake fluid is cloudy, then it's got water moisture and should be purged completely.
Buy a tube of dielectric grease and put a healthy dab on all your electrical connectors.
It's great for water proofing and prevents corrosion of the contacts. Also makes the connect/disconnect easier as well.
Besides changing out all your fluids for fresh, check all your radiator hose clamps to ensure they're tight. Might also need to have your valve clearances checked if the last interval is unknown. Replace the air filters as well.
In other words, a complete service plus close visual inspection.
First off, it sounds like your rear caliper will need to be rebuilt or replaced.
The piston is sticking in the bore causing the brake drag you mentioned.
If the caliper piston bore is too badly corroded, it will probably be best to replace the rear caliper. If the bore isn't too badly corroded, then rebuilding the caliper may suffice.
If the rear is that bad, you may need to closely check the fronts as well.
If the brake fluid is cloudy, then it's got water moisture and should be purged completely.
Buy a tube of dielectric grease and put a healthy dab on all your electrical connectors.
It's great for water proofing and prevents corrosion of the contacts. Also makes the connect/disconnect easier as well.
Besides changing out all your fluids for fresh, check all your radiator hose clamps to ensure they're tight. Might also need to have your valve clearances checked if the last interval is unknown. Replace the air filters as well.
In other words, a complete service plus close visual inspection.