My old rover colt 5 is significantly quicker then it used to be so I thought I had better open up the gear box before it inevitably goes bang. Ideally I would fill it with something like a 90 weight gear oil but I dont think the seals have what it takes to hold the oil in. So which grease should I be filling it with? The only grease I have on hand is marine wheel bearing grease but it feels thinner then the existing grease that is in it. On the other hand the existing grease may have simply hardened over time.

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